i965/fs: Extend SEL peephole to handle only matching MOVs.

i965/fs: Extend SEL peephole to handle only matching MOVs.

Before this patch, the following code would not be optimized even though
the first two instructions were common to the then and else blocks:

   (+f0) IF
   MOV dst0 ...
   MOV dst1 ...
   MOV dst2 ...
   ELSE
   MOV dst0 ...
   MOV dst1 ...
   MOV dst3 ...
   ENDIF

This commit extends the peephole to handle this case.

No shader-db changes.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>