drm: Add WARN_ON_ONCE()

Obtained-from: OpenBSD
drm/i915: Add hardware context support

This feature is required by Mesa 9.2+

Inspired-by: Jean-Sébastien Pédron's FreeBSD HW context patch
kernel: Remove some lonely tabs.
kernel: Use NULL for pointers in DRIVER_MODULE().
kernel/nexus: Use __func__.
kernel/i386: Add SMAP type constants.
kernel/nexus: Tabify the RAM driver.
nexus/x86_64: Add a description to the RAM driver but quiet it.

Also, some more whitespace cleanup.

Patch-by: profmakx
kernel/i386: Add RAM driver for i386.