staging: hikey9xx: add build for the Kirin 970 PHY driver

Add the needed bits in order to build the Kirin 970 PHY
driver.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/60aae73e91348430e940638cf9668a0a63a85c1c.1600338981.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>