freedreno/ir3: convert back to 32-bit values for half constant registers.

freedreno/ir3: convert back to 32-bit values for half constant registers.

It seems to handle only 32-bit values for half constant registers
within floating point opcodes according to the blob driver.
So we need to convert back to 32-bit values from 16-bit values, when a
lower precision pass is in effect.

Signed-off-by: Rob Clark <robdclark@chromium.org>