freedreno: prep work for timestamp queries

freedreno: prep work for timestamp queries

We need "NULL" state to be a valid bit in the bitmask, because timestamp
queries are not restricted to draw/etc stages (ie. the only commands to
submit may just be to read the timestamp).  And just because there are
no draws, isn't a reason to skip the flush and return zero.

Signed-off-by: Rob Clark <robdclark@gmail.com>