regulator: pfuze100: add .is_enable() for pfuze100_swb_regulator_ops

regulator: pfuze100: add .is_enable() for pfuze100_swb_regulator_ops

[ Upstream commit 0b01fd3d40fe6402e5fa3b491ef23109feb1aaa5 ]

If is_enabled() is not defined, regulator core will assume
this regulator is already enabled, then it can NOT be really
enabled after disabled.

Based on Li Jun's patch from the NXP kernel tree.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>