ppc: POWER7 has lq/stq instructions and stq need to check ISA

The PPC_64BX instruction flag is used for a couple of newer
instructions currently on POWER8 but our implementation for
them works for POWER7 too (and already does the proper checking
of what is permitted) with one exception: stq needs to check
the ISA version.

This fixes the latter and add the instructions to POWER7

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
