Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Extend dim's hack from r228978: not only clang but gcc on non-x86 platforms
warns about unused variables in this code, so always add -Wno-unused to
the warning flags. Why gcc on x86 *doesn't* warn about this, I will never
know. The code itself should probably be fixed at some point.

For several files in sys/dev/drm, disable -Wunused-value when building
with clang. There are several macros in these files that return values,
and in some cases nothing is done with them, but it is completely
harmless. For some other files, also disable -Wconstant-conversion,
since that triggers a false positive with the DMA_BIT_MASK() macro.

MFC after: 1 week

bsd.kmod.mk does not deal with manpages anymore.

Update the DRM to latest from DRI CVS. This is approximately the version
included in XFree86 4.3, but includes some fixes. Notable changes include
Radeon 8500-9100 support, PCI Radeon/Rage 128 support, transform & lighting
support for Radeons, and vblank syncing support for r128, radeon, and mga.
The gamma driver was removed due to lack of any users.

Zap KMODDEPS entries so that people do not wonder why it isn't working on
-current.

Apolgies to: anhold

Hook the DRM up to the build and add it to NOTES.

Approved by: des

Add makefiles for DRM modules

Approved by: des