staging: mfd: hi6421-spmi-pmic: change namespace on its functions

Rename the functions used internally inside the driver in
order for them to follow the driver's name.

While here, get rid of some unused definitions at the
header file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/bfa8bf33f71612b1511d73269ca242d0d4e70940.1597647359.git.mchehab+huawei@kernel.org


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