rs6000: Clean up the cstore code a bit
"register_operand" was a bit confusing. Also some other minor cleanups.
* (cstore<mode>4_unsigned): Use gpc_reg_operand instead of
register_operand. Remove empty constraints. Use std::swap.
(cstore_si_as_di, cstore<mode>4_signed_imm,
cstore<mode>4_unsigned_imm, cstore<mode>4 for GPR): Use
gpc_reg_operand instead of register_operand.
(cstore<mode>4 for FP): Use gpc_reg_operand instead of
register_operand. Remove empty constraints.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@231287 138bc75d-0d04-0410-961f-82ee72b054a4