powerpc: Fix iseries drivers build failure without CONFIG_VIOPATH

iSeries dependent drivers fail to build, when CONFIG_VIOPATH is disabled.

Fix the problem by making those drivers select it.

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>