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
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)
