- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

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

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

Add reader/writer lock around mem_range_attr_get() and mem_range_attr_set().
Compile sys/dev/mem/memutil.c for all supported platforms and remove now
unnecessary dev_mem_md_init(). Consistently define mem_range_softc from
mem.c for all platforms. Add missing #include guards for machine/memdev.h
and sys/memrange.h. Clean up some nearby style(9) nits.

MFC after: 1 month

Add a memory-range interface to /dev/mem on PowerPC using PAT attributes.
Unlike actual MTRR, this only controls the mapping attributes for
subsequent mmap() of /dev/mem. Nonetheless, the support is sufficiently
MTRR-like that Xorg can use it, which translates into an enormous increase
in graphics performance on PowerPC.

MFC after: 2 weeks

Remove the unused M_MEMDEV from the kernel.

The M_MEMDEV memory allocation pool does not seem to be used. We can
live without it.

Approved by: philip (mentor)

Remove the unused major/minor numbers from iodev and memdev.

Now that st_rdev is being automatically generated by the kernel, there
is no need to define static major/minor numbers for the iodev and
memdev. We still need the minor numbers for the memdev, however, to
distinguish between /dev/mem and /dev/kmem.

Approved by: philip (mentor)

Add /dev/mem and /dev/kmem to powerpc.

Approved by: grehan (mentor)