staging: hikey9xx: hi6421-spmi-pmic: document registers

Make it clearer about how the IRQ registers are filled by adding
a table with them, with two macros used to calculate the mask
register.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/10f52ec0a8346fb883245344886c44714c859cd1.1611949675.git.mchehab+huawei@kernel.org


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