regulator: tps65910: wire up sleep control configuration

This enables configuring the PMIC's sleep mode via device-tree.

A pointer indirection to sleep mode data is removed, as it simplifies
the implementation slightly. In current kernel tree, platform data
structure is not used outside MFD cell drivers.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Mark Brown <broonie@kernel.org>