cmd/internal/obj: reorg ppc64 MOV* optab entries and remove unused classes

C_LECON and C_SECON classifications are not generated on ppc64, however
there are many optab entries which match against them. Remove them to
resolve their related TODOs.

Likewise, reorder the optab entries for better readability.

Change-Id: I894a209a148014e5aa438b7303e7fbdda4727c4e
Reviewed-on: https://go-review.googlesource.com/c/go/+/307429


Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Carlos Eduardo Seo <carlos.seo@linaro.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Trust: Carlos Eduardo Seo <carlos.seo@linaro.org>