mfd: tps65218.c: Add input voltage options

These options apply to all regulators in this chip.

ti,strict-supply-voltage-supervision:
  Set STRICT flag in CONFIG1
ti,under-voltage-limit-microvolt:
  Select 2.75, 2.95, 3.25 or 3.35 V UVLO in CONFIG1
ti,under-voltage-hyst-microvolt:
  Select 200mV or 400mV UVLOHYS in CONFIG2

Signed-off-by: Christian Hohnstaedt <Christian.Hohnstaedt@wago.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>