firmware: arm_scpi: Move power-domain driver to the pmdomain dir

To simplify with maintenance let's move the Arm SCPI power-domain driver
to the new pmdomain directory. Note this is different from and precedes
the new Arm SCMI protocol.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20231123120847.2825444-2-sudeep.holla@arm.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>