power: reset: Add TPS65086 restart driver

The only way to reset the BeagleV Starlight v0.9 board[1] properly is to
tell the PMIC to reset itself which will then assert the external reset
lines of the SoC, USB hub and ethernet phy.

This adds a driver to register a reset handler to do just that.

[1] https://github.com/beagleboard/beaglev-starlight



Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>