regulator: pfuze100-regulator: add coin support

Add support for PF0200 coin cell/super capacitor charger which works as
a current limited voltage source via the LICELL pin. When VIN goes below
a certain threshold LICELL is used to provide power for VSNVS which is
usually used to hold up secure non-volatile storage and the real-time
clock on the SoC.

Signed-off-by: George McCollister <george.mccollister@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>