drm/i915: Restore pci_enable_busmaster() call in the init path

drm/i915: Restore pci_enable_busmaster() call in the init path

This fixes a GPU hang on i945GM.

While here, merge some minor fixes to DRM core and i915:
  * Remove obsolete drm_agp_*_memory() prototypes
  * Fix comment in drm_fops.c (outisde -> outside)
  * Fix some formatting issues in drm_stub.c (spaces -> tabs)

Approved by:	re (marius)
MFC of:		r288653, r288952, r293851
Submitted by:	<s3erios@gmail.com>
Differential Revision:	https://reviews.freebsd.org/D3413

git-svn-id: svn://svn.freebsd.org/base/stable/10@295623 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f