Prefer fullscreen clears on Qualcomm/GL

Adds Qualcomm to the set of GL devices on which we prefer fullscreen
clears.

Renames fullscreenClearIsFree in GrCaps to preferFullscreenClears.

Replaces 'bool canIgnoreClip' on GrRenderTargetContext::clear with an
enum.

Bug: skia:
Change-Id: I5b30298c4d0b092c398b9fea6060f3e2bea91e46
Reviewed-on: https://skia-review.googlesource.com/83060
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
22 files changed