The operands for MAQ_SA_W.PHL/MAQ_SA_W.PHR must in specified format.
Otherwise, the results are unpredictable. Once the operands were corrected
in the tests (part of this change), a bug in mipsdsp_mul_q15_q15 became
visible.
This change corrects the tests for MAQ_SA_W.PHL/MAQ_SA_W.PHR and fixes
sign-related issue in mipsdsp_mul_q15_q15. It also removes unnecessary
comment.
Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>