drm2: a few minor fixes after r280183

drm2: a few minor fixes after r280183

* Remove obsolete drm_agp_*_memory() prototypes.
* Fix comment in drm_fops.c (outisde -> outside).
* Fix some formatting issues in drm_stub.c (spaces -> tabs).
* Add missing case statement (gen == 3) in intel_gpu_reset().
* Restore pci_enable_busmaster() call in the init path (fixes gpu hang on i945GM).
* Replace M_WAITOK with M_NOWAIT when the return value of malloc is checked (may be incorrect).

Submitted by:	<s3erios@gmail.com>
Reviewed by:	dumbbell
Approved by:	dumbbell
Differential Revision:	https://reviews.freebsd.org/D3413