lima/ppir: lower ffma in ppir
Since we cannot handle ffma in ppir, lower it on nir level already.
TGSI is used as the preferred IR, st_glsl_to_tgsi creates a MAD op within the
WPOS_Y_TRANSFORM action which is lowered to ffma later on.
nir_lower_wpos_ytransform() has dropped ffma already. Since ppir doesn't handle ffma yet,
we use nir to lower it.
This lowers ffma ops in pp in general of course, the above is just how i ran into it.