Revert r338177, r338176, r338175, r338174, r338172

After long consultations with re@, core members and mmacy, revert
these changes. Followup changes will be made to mark them as
deprecated and prent a message about where to find the up-to-date
driver.  Followup commits will be made to make this clear in the
installer. Followup commits to reduce POLA in ways we're still
exploring.

It's anticipated that after the freeze, this will be removed in
13-current (with the residual of the drm2 code copied to
sys/arm/dev/drm2 for the TEGRA port's use w/o the intel or
radeon drivers).

Due to the impending freeze, there was no formal core vote for
this. I've been talking to different core members all day, as well as
Matt Macey and Glen Barber. Nobody is completely happy, all are
grudgingly going along with this. Work is in progress to mitigate
the negative effects as much as possible.

Requested by: re@ (gjb, rgrimes)

As discussed on the MLs drm2 conflicts with the ports' version and there
is no upstream for most if not all of drm. Both have been merged in to
a single port.

Users on powerpc, 32-bit hardware, or with GPUs predating Radeon
and i915 will need to install the graphics/drm-legacy-kmod. All
other users should be able to use one of the LinuxKPI-based ports:
graphics/drm-stable-kmod, graphics/drm-next-kmod, graphics/drm-devel-kmod.

MFC: never
Approved by: core@

* Remove obsolete drm_agp_*_memory() prototypes.
* Fix comment in drm_fops.c (outisde -> outside).
* Fix some formatting issues in drm_stub.c (spaces -> tabs).
* Add missing case statement (gen == 3) in intel_gpu_reset().
* Restore pci_enable_busmaster() call in the init path (fixes gpu hang on i945GM).
* Replace M_WAITOK with M_NOWAIT when the return value of malloc is checked (may be incorrect).

Submitted by:	<s3erios@gmail.com>
Reviewed by:	dumbbell
Approved by:	dumbbell
Differential Revision:	https://reviews.freebsd.org/D3413

This update brings few features:
    o  Support for the setmaster/dropmaster ioctls. For instance, they
       are used to run multiple X servers simultaneously.
    o  Support for minor devices. The only user-visible change is a new
       entry in /dev/dri but it is useless at the moment. This is a
       first step to support render nodes [1].

The main benefit is to greatly reduce the diff with Linux (at the
expense of an unreadable commit diff). Hopefully, next upgrades will be
easier.

No updates were made to the drivers, beside adapting them to API
changes.

[1] https://en.wikipedia.org/wiki/Direct_Rendering_Manager#Render_nodes

Tested by:	Many people
MFC after:	1 month
Relnotes:	yes

1) It is not useful to call "devfs_clear_cdevpriv()" from
"d_close" callbacks, hence for example read, write, ioctl and
so on might be sleeping at the time of "d_close" being called
and then then freed private data can still be accessed.
Examples: dtrace, linux_compat, ksyms (all fixed by this patch)

2) In sys/dev/drm* there are some cases in which memory will
be freed twice, if open fails, first by code in the open
routine, secondly by the cdevpriv destructor. Move registration
of the cdevpriv to the end of the drm open routines.

3) devfs_clear_cdevpriv() is not called if the "d_open" callback
registered cdevpriv data and the "d_open" callback function
returned an error. Fix this.

Discussed with:	phk
MFC after:	2 weeks

works with new generations of GPUs (IronLake, SandyBridge and
supposedly IvyBridge).

The driver is not connected to the build yet.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week