i965/fs: fix indirect load DF uniforms on BSW/BXT

i965/fs: fix indirect load DF uniforms on BSW/BXT

The lowered BSW/BXT indirect move instructions had incorrect
source types, which luckily wasn't causing incorrect assembly to be
generated due to the bug fixed in the next patch, but would have
confused the remaining back-end IR infrastructure due to the mismatch
between the IR source types and the emitted machine code.

v2:
- Improve commit log (Curro)
- Fix read_size (Curro)
- Fix DF uniform array detection in assign_constant_locations() when
  it is acceded with 32-bit MOV_INDIRECTs in BSW/BXT.

v3:
- Move changes in assign_constant_locations() to other patch.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Cc: "17.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>