In the case where there's no damage monitor on the drawable, we look
that fact up twice: once before rendering to decide whether to compute
damage, and again after to decide whether to append it. This is wasted
effort, as the layer below us is effectively not allowed to change
whether there's a damage monitor for the drawable, but there's no way
the compiler can know that.

Instead, look it up once up front, and change the check macros and
damageRegionProcessPending to take a damage not a drawable.

v2: Explicitly pass pDamage to the macros as well (Michel Dänzer)

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>