Use "mr" and make a few other tweaks in PowerPC ncg table.

Use "mr" and make a few other tweaks in PowerPC ncg table.

Use extended "mr" instead of basic "or" to move registers.  Both "mr"
and "or" encode the same machine instruction.  With "mr", I can more
easily search the assembly output for register moves.

Fold several stacking rules into a single rule ANY_BHW-REG to STACK.

Remove the EM patterns for loc mlu $2==2 and loc slu.  The first
pattern had the wrong size (should be $2==4, not $2==2).  Both
patterns were redundant.  They rewrote loc mlu as loc mli and loc slu
as loc sli, but this table doesn't have patterns for loc mli or loc
sli, so it is enough to rewrite mlu as mli and slu as sli.