drm/radeon: Add 32bit ioctls support

This allows to run 32bit applications on a 64bit host. This was tested
successfully with Wine (emulators/i386-wine-devel) and StarCraft II.

Submitted by:	Jan Kokemüller <jan.kokemueller@gmail.com>
MFC after:	1 week
Make this manpage ready for hardware notes generation, add more Xrefs and perform
general cleanup.

In particular, don't claim rsu(4) devices can be configured with hostname(1)...

MFC after:	1 week
Add rsu(4) to the hardware notes.

MFC after:	1 week