'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

- Rename PCPU_LAZY_INC into PCPU_INC
- Add the PCPU_ADD interface which just does an add on the pcpu member
  given a specific value.

Note that for most architectures PCPU_INC and PCPU_ADD are not safe.
This is a point that needs some discussions/work in the next days.

Reviewed by: alc, bde
Approved by: jeff (mentor)

header file.  Reimplement PCPU_LAZY_INC() on amd64 and i386 making it
atomic with respect to interrupts.

Reviewed by: bde, jhb

per-CPU memory. This allows for interrupt handling on multiple CPUs.

Obtained from: NetBSD

Obtained from:	NetBSD (portions)

Highlights include:
- New low-level trap code from NetBSD.  The high level code still needs a lot
  of work.
- Fixes for some pmap handling in thread switching.
- The kernel will now get to attempting to jump into init in user mode.  There
  are some pmap/trap issues which prevent it from actually getting there though.

Obtained from:	NetBSD (parts)

- The MI portions of struct globaldata have been consolidated into a MI
  struct pcpu.  The MD per-CPU data are specified via a macro defined in
  machine/pcpu.h.  A macro was chosen over a struct mdpcpu so that the
  interface would be cleaner (PCPU_GET(my_md_field) vs.
  PCPU_GET(md.md_my_md_field)).
- All references to globaldata are changed to pcpu instead.  In a UP kernel,
  this data was stored as global variables which is where the original name
  came from.  In an SMP world this data is per-CPU and ideally private to each
  CPU outside of the context of debuggers.  This also included combining
  machine/globaldata.h and machine/globals.h into machine/pcpu.h.
- The pointer to the thread using the FPU on i386 was renamed from
  npxthread to fpcurthread to be identical with other architectures.
- Make the show pcpu ddb command MI with a MD callout to display MD
  fields.
- The globaldata_register() function was renamed to pcpu_init() and now
  init's MI fields of a struct pcpu in addition to registering it with
  the internal array and list.
- A pcpu_destroy() function was added to remove a struct pcpu from the
  internal array and list.

Tested on:	alpha, i386
Reviewed by:	peter, jake

  will be private to each CPU.
- Re-style(9) the globaldata structures.  There really needs to be a MI
  struct pcpu that has a MD struct mdpcpu member at some point.