firmware: scmi: voltage regulator

Implement voltage regulators interfaced by the SCMI voltage domain
protocol. The DT bindings are defined in the Linux kernel since
SCMI voltage domain and regulators patches [1] and [2] integration
in v5.11-rc7.

Link: [1] https://github.com/torvalds/linux/commit/0f80fcec08e9c50b8d2992cf26495673765ebaba
Link: [2] https://github.com/torvalds/linux/commit/2add5cacff3531e54c50b0832128299faa9f0563
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
6 files changed