mfd: palmas: Add tps65917 support

Add tps65917 PMIC support. tps65917 is a subset of palmas PMIC.
Some of the register definitions and the interrupt mappings
are different.

Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>