only need to hoist one register per tbl imm

As written it was hoisting one register per tbl instruction use, which
was both correct and fast, but using more registers than necessary.  We
only need one table mask for each unique Op::bytes control value.

Caught this looking at the profile for srcover_i32, which uses each of
two distinct bytes control values twice, once for the src pixel and once
for dst.

Change-Id: I42f8611b23c0258369e8aaadd75fc484d1e9cb35
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229397
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed