refactor(stpmic1): use BIT and GENMASK helpers
refactor(stpmic1): use BIT and GENMASK helpers

Use BIT and GENMASK macros to ease stpmic1.h reading.

Change-Id: I808a62818d4188bb2f3686ab37518d369b6c41cb
Signed-off-by: Yann Gautier <e753f6969c288905606e3c07464886d4f1fc1be0@foss.st.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware