i965/fs: Print "+reladdr" on variably-indexed uniform arrays.

i965/fs: Print "+reladdr" on variably-indexed uniform arrays.

Previously, dump_instruction() would print output such as:
   {  2}    3: mov vgrf1:F, u0:F
   {  3}    4: mov vgrf7:F, u0:F
   {  4}    5: mov vgrf8:F, u0:F
which looked like either a scalar access or perhaps a constant-indexed
access of element 0, when it was really a variable index.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>