staging: spmi: add Hikey 970 SPMI controller driver

Add the SPMI controller code required to use the Kirin 970
SPMI bus.

[mchehab+huawei@kernel.org: added just the SPMI controller on this patch]

The complete patch is at:

	https://github.com/96boards-hikey/linux/commit/08464419fba2Signed-off-by: Mayulong <mayulong1@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b4810f476e41e7de4efdf28b42472ae4ffe7defe.1597647359.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>