drm - Stabilize broadwell and improve skylake
* The issue was primarily the bitops on longs were all wrong. '1 << N'
returns an integer (even if N is a long), so those had to be 1L or 1LU.
There were also some missing parenthesis in the bit test code.
* Throw in one fix from Linux, but I think its basically a NOP when DMAPs
are used (and we use DMAPs).
* Add some code to catch a particular failure condition by locking up X
in a while/tsleep loop instead of crashing outright, allowing a remote
login to kgdb the live system.