power: pmic: pca9450: Add support for reset status

power: pmic: pca9450: Add support for reset status

PCA9450 PMIC supports reading the reset status from the PWRON_STAT
register. Bits 7-4 give indication of the PMIC reset cause:

 - PWRON (BIT7) - Power ON triggered by PMIC_ON_REQ input line,
 - WDOGB (BIT6) - Boot after cold reset by WDOGB pin (watchdog reset),
 - SW_RST (BIT5) - Boot after cold reset initiated by the software,
 - PMIC_RST (BIT4) - Boot after PMIC_RST_B input line trigger.

Add support for reading reset status via the sysreset framework in a
convenient printable format.

Signed-off-by: Primoz Fiser <primoz.fiser@norik.com>
Reviewed-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>