mfd: stpmic1: Fixup main control register and bits naming

Fixup main control register and bits naming so the match the naming from
the datasheet.

https://www.st.com/resource/en/datasheet/stpmic1.pdf

Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230602062426.3947116-1-sean@geanix.com

mfd: stpmic1: Add STPMIC1 driver

STPMIC1 is a PMIC from STMicroelectronics. The STPMIC1 integrates 10
regulators, 3 power switches, a watchdog and an input for a power on key.

Signed-off-by: Pascal Paillet <p.paillet@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>