hppa: Fix (plus (plus (mult (a) (mem_shadd_constant)) (b)) (c)) optimization

The constant C must be an integral multiple of the shift value in
the above optimization.  Non integral values can occur evaluating
IMAGPART_EXPR when the shadd constant is 8 and we have SFmode.

2024-08-06  John David Anglin  <danglin@gcc.gnu.org>

gcc/ChangeLog:

	PR target/113384
	* config/pa/pa.cc (hppa_legitimize_address): Add check to
	ensure constant is an integral multiple of shift the value.