staging: mfd: hi6421-spmi-pmic: cleanup OF properties

Simplify the names of the DT properties and do some cleanups,
in order to better document them.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/24ffcd28a17ee7b0940d8aabef556d172d5feddf.1597647359.git.mchehab+huawei@kernel.org


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