nouveau: codegen: combineLd/St do not combine indirect loads

nouveau: codegen: combineLd/St do not combine indirect loads

combineLd/St would combine, i.e. :

st  u32 # g[$r2+0x0] $r2
st  u32 # g[$r2+0x4] $r3

into:

st  u64 # g[$r2+0x0] $r2d

But this is only valid if r2 contains an 8 byte aligned address,
which is not guaranteed for compute shaders

This commit checks for src0 dim 0 not being indirect when combining
loads / stores as combining indirect loads / stores may break alignment
rules.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>