msm: qpnp-power-on: remove pon_power_off_type member PON_POWER_OFF_UVLO

Currently, PON_POWER_OFF_UVLO is defined in enum pon_power_off_type.
However, this enum is used to list the possible power off types that can be
passed into qpnp_pon_system_pwr_off. UVLO is not one of the types that can
be passed to qpnp_pon_system_pwr_off. Hence remove PON_POWER_OFF_UVLO from
enum pon_power_off_type.

Change-Id: Ibf6cde349da4d27bff3250618ed91baca926bce2
Signed-off-by: Ke Liu <keliu@codeaurora.org>