powerpc: Add missing modes to P9 if_then_elses [PR121501]

powerpc: Add missing modes to P9 if_then_elses [PR121501]

These patterns had one (if_then_else ...) nested within another.
The outer if_then_else had SImode, which means that the "then"
and "else" should also be SImode (unless they're const_ints).
However, the inner if_then_else was modeless, which led to an
assertion failure when trying to take a subreg of it.

gcc/
	PR target/121501
	* config/rs6000/rs6000.md (cmprb, setb_signed, setb_unsigned)
	(cmprb2, cmpeqb): Add missing modes to nested if_then_elses.