MFC r277487:

MFC r277487:
An update for the i915 GPU driver, which brings the code up to Linux
commit 4d93914ae3db4a897ead4b.

MFC r277959 (by adrian):
Fix backlight for ivybridge based laptops (and whatever else comes through
this codepath.)

MFC r278146:
Do not attach to the unsupported chipsets, unless magic tunable is
frobbed.

MFC r278147, r278148:
Fix sign for the error code returned from the driver-specific code.

MFC r278152:
Do not access gmbus_ports array past its end.

MFC r278159 (by emaste):
Remove duplicate intel_fbc_enabled prototype.

git-svn-id: svn://svn.freebsd.org/base/stable/10@280369 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f