freedreno/ir3: fix pos_regid > max_reg

freedreno/ir3: fix pos_regid > max_reg

We can't (or don't know how to) turn this off.  But it can end up being
stored to a higher reg # than what the shader uses, leading to
corruption.

Also we currently aren't clever enough to turn off frag_coord/frag_face
if the input is dead-code, so just fixup max_reg/max_half_reg.  Re-org
this a bit so both vp and fp reg footprint fixup are called by a common
fxn used also by ir3_cmdline.  Also add a few more output lines for
ir3_cmdline to make it easier to see what is going on.

Signed-off-by: Rob Clark <robclark@freedesktop.org>