DRM_*MEMORYBARRIER we had were related to an MMIO space. This means
arch-specific code on the BSDs, unfortunately. Also add
DRM_MEMORYBARRIER() and change the DRM_READMEMORYBARRIER()s that used
to be read/write barriers to it.
1) Remove redundant header inclusion
2) Silence bitop on non-long argument warnings (change int to long)
3) Move to ISO C (gcc 2.6) initializers (accepted by older gccs also) All
of these are syntax changes that should not impact functionality.