staging: hikey9xx: spmi driver: convert to regmap

Instead of doing its own SPMI I/O implementation, use the
already-existing regmap one.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/7084885f3007ca5daf0d5bc85d038e26ee82dc0d.1611949675.git.mchehab+huawei@kernel.org


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