When querying the GTFIFOCTL register to check the FIFO space, the read value
must be masked. The operation is repeated explicitly in several places. This
change refactors the read-and-mask code into a function call.
v2: rebased on top of Mika's forcewake patch set, specifically:
[PATCH 8/8] drm/i915: Enum forcewake domains and domain identifiers
Change-Id: Id1a9f3785cb20b82d4caa330c37b31e4e384a3ef Signed-off-by: Dave Gordon <david.s.gordon@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>