cmd/internal/obj: remove param element from ppc64 optab

cmd/internal/obj: remove param element from ppc64 optab

This is rarely used, and is implied based on the
memory type of the operand.  This is a step towards
simplifying the MOV* pseudo opcodes on ppc64.

Similarly, remove the bogus param value from AVMULESB.

Change-Id: Ibad4d045ec6d8c5163a468b2db1dfb762ef674ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/300177
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Trust: Ian Lance Taylor <iant@golang.org>