sysreset: implement TPS80031 sysreset functions

TPS80031/TPS80032 PMICs have embedded power control functions
used by some device to initiane device power off. Implement it as
sysreset driver.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>

power: pmic: add the base TPS80031 PMIC support

Add support to bind the regulators/child nodes with the pmic.
Also adds the pmic i2c based read/write functions to access pmic
registers.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>