Fix so that color changes are not lost when the video mode changes.

PR:             bin/83553
Submitted by:   Dan Lukes <dan at obluda dot cz>
Approved by:	re (scottl)
Reminded by:	delphij

Approved by:	re (blanket)

24, and 32 bit modes.  To use that, syscons(4) must be built with
the compile time option 'options SC_PIXEL_MODE', and VESA support (a.k.a.
vesa.ko) must be either loaded, or be compiled into the kernel.

Do not return EINVAL when the mouse state is changed to what it already is,
which seems to cause problems when you have two mice attached, and
applications are not likely obtain useful information through the EINVAL
caused by showing the mouse pointer twice.

Teach vidcontrol(8) about mode names like MODE_<NUMBER>, where <NUMBER> is
the video mode number from the vidcontrol -i mode output.  Also, revert the
video mode if something fails.

Obtained from:	DragonFlyBSD
Discussed at:	current@ with patch attached [1]
PR:		kern/71142 [2]
Submitted by:	Xuefeng DENG <dsnofe at msn com> [1],
		Cyrille Lefevre <cyrille dot lefevre at laposte dot net> [2]

Noticed by:	stefanf
Reviewed by:	diff(1)

	- Use foo(void) instead of foo().
	- Use static where applicable.
	- Apply more const's when passing parameters
	- signed/unsigned madness
	- Avoid namespace collision by adding underscores.
	- For 64-bit architectures, use %zx instead of %x
	  when necessary.
	- When storing constants, use const instead of
	  variable.
	- Bump WARNS?= from 2 to 6

is compiled in the kernel.  Also add some useful xrefs to lock(1).