The driver tries to initialize all possible regulators from the DT, then
match the external regulators with each channel and then release all unused
regulators.

We can change the logic a bit to initialize regulators only when at least
one channel needs them.

This change creates a mx25_gcq_ext_regulator_setup() function that is
called only for the external regulators. If there's already a reference to
an external regulator, the function will just exit early with no error.

This way, the driver doesn't need to keep any track of these regulators
during init.
Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210625074325.9237-1-aardelean@deviqon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>