i965/skl: skip fast clears for certain surface formats

i965/skl: skip fast clears for certain surface formats

Some of the information originally in this commit message is now in the patch
before this.

SKL adds compressible render targets and as a result mutates some of the
programming for fast clears and resolves. There is a new internal surface type
called the CCS. The old AUX_MCS bit becomes AUX_CCS_D. "Auxiliary Surfaces For
Sampled Tiled Resource".

The formats which are supported are defined in the table titled "Render Target
Surface Types [SKL+]". There is no PRM yet to reference. The previously
implemented helper function already does the right thing provided the table is
correct.

v2: Use better English in commit message (Matt)
s/compressable/compressible/ (Matt)
Don't compare bools to true (Matt)
Use the helper function and don't increase the context size - this is mostly
implemented in the patch just before this (Chad, Neil)
Remove an "invalid" assert (Chad)
Fix assertion to check num_samples > 1, instead of num_samples (Chad)

v3:
Use Matt's code as Requested-by: Chad. I didn't even look at it since Chad said
he was fine with that, and presumably Matt is fine with it.

v4: Use better quote from spec (Topi)

Cc: Chad Versace <chad.versace@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>