staging: hikey9xx: split hi6421v600 irq into a separate driver

Per MFD subsystem requirements, split the IRQ part of the
driver into a separate one with just the IRQ handling code
and the powerkey support.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/709e01c9ffafe6cd0ecb23336b44f9bcde2b5bc2.1626515862.git.mchehab+huawei@kernel.org


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