[PowerPC] Don't use rldicl for PPC32

According to https://www.ibm.com/support/knowledgecenter/ssw_aix_72/assembler/idalangref_rldicl_rletdw_instrs.html rldicl should not be used when targeting 32bit CPUs.

Reviewed By: #powerpc, nemanjai, MaskRay

Differential Revision: https://reviews.llvm.org/D77946