Input: bbnsm_pwrkey - add bbnsm power key support

The ON/OFF logic inside the BBNSM allows for connecting directly
into a PMIC or other voltage regulator device. The module has an
button input signal and a wakeup request input signal. It also
has two interrupts (set_pwr_off_irq and set_pwr_on_irq) and an
active-low PMIC enable (pmic_en_b) output.

Add the power key support for the ON/OFF button function found in
BBNSM module.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20230215024117.3357341-2-ping.bai@nxp.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>