drm/i915: i915_wire_page is shmem_read_mapping_page()

* Rename it and change its return type to be 100% compatible with the
same function from Linux 3.8.13.

* Also change the functions using it a bit to be more like what they
are in Linux. Variable names were changed and *BSD-specific APIs
unnecessarily introduced during the original port of this code from
Linux to FreeBSD.
drm: Add linux/shmem_fs.h

shmem_read_mapping_page() is part of the public Linux API. Make it
accessible from linux/shmem_fs.h
make.conf.5: Fix date.
cpucontrol.8: Use Mt for email addresses.