i965/fs: Set force_uncompressed and force_sechalf on samplepos setup.

i965/fs: Set force_uncompressed and force_sechalf on samplepos setup.

gen8_fs_generator uses these to decide whether to set the execution size
to 8 or 16, so we incorrectly made both of these MOVs the full width in
SIMD16 shaders.  (It happened to work out on Gen4-7.)

Setting them should also help inform optimization passes what's really
going on, which could help avoid bugs.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: mesa-stable@lists.freedesktop.org