[SRU utopic] LP#1386695 -- GPU lockups on resume

[Andy Whitcroft]

We have GPU lockups reported on Utopic on resume from suspend.  The
original reporter bisected the fix out of v3.17.  Following this email
are two patches, the first foundational, the second the actual fix for
this issue (essentially accesses racing with device BAR resume).

I have produced test kernels with these applied which have been
validated by the OR.  Proposing for SRU to utopic.

-apw