test: enable more memcombine tests for ppc64le
test: enable more memcombine tests for ppc64le

This enables more of the testcases in memcombine for ppc64le,
and adds more detail to some existing.

Change-Id: Ic522a1175bed682b546909c96f9ea758f8db247c
Reviewed-on: https://go-review.googlesource.com/c/go/+/174737
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,josharian/go,cloudflare/go,josharian/go,akutz/go,josharian/go,akutz/go,cloudflare/go,nawawi/go,golang/go,josharian/go,cloudflare/go,josharian/go,cloudflare/go,josharian/go,akutz/go,golang/go,akutz/go,nawawi/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,josharian/go,josharian/go,cloudflare/go,nawawi/go,nawawi/go,golang/go,golang/go,akutz/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,golang/go,CAFxX/go,golang/go,golang/go,akutz/go,CAFxX/go