freedreno/ir3: start dealing with half-precision

freedreno/ir3: start dealing with half-precision

Some instructions, assume src and/or dst is half-precision based on a
type field (ie. f32/s32/u32 are full precision but others are half
precision).  So add some code to sanity check the src/dst registers to
catch mixups.

Also propagate half-precision flag for SSA sources.  The instruction
consuming a SSA value needs to be of the same type as the one producing
it.

This is probably not complete half-precision support, but a useful first
step.  We do still need to add support for nir alu instructions for
converting between half/full precision.

Signed-off-by: Rob Clark <robdclark@gmail.com>