i965/fs: Don't use brw_imm_* unnecessarily.

i965/fs: Don't use brw_imm_* unnecessarily.

Using brw_imm_* creates a source with file=HW_REG, and the scheduler
inserts barrier dependencies when it sees HW_REG. None of these are
hardware-registers in the sense that they're special and scheduling
shouldn't touch them. A few of the modified cases already have HW_REGs
for other sources, so it won't allow extra flexibility in some cases.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>