regulator: add SCMI driver

Add a simple regulator based on SCMI Voltage Domain Protocol.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
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v6 --> v7
- add proper blank lines between semantic blocks
- fix return value on error path of scmi_reg_is_enabled()
- use generic Failure message on err path of info_get()
- fix comment containing apostrophe

v3 --> v4
- using of_match_full_name core regulator flag
- avoid coccinelle falde complaints about pointer-sized allocations

v2 --> v3
- remove multiple linear mappings support
- removed duplicated voltage name printout
- added a few comments
- simplified return path in scmi_reg_set_voltage_sel()

v1 --> v2
- removed duplicate regulator naming
- removed redundant .get/set_voltage ops: only _sel variants implemented
- removed condexpr on fail path to increase readability

v0 --> v1
- fixed init_data constraint parsing
- fixes for v5.8 (linear_range.h)
- fixed commit message content and subject line format
- factored out SCMI core specific changes to distinct patch
- reworked Kconfig and Makefile to keep proper alphabetic order
- fixed SPDX comment style
- removed unneeded inline functions
- reworked conditionals for legibility
- fixed some return paths to properly report SCMI original errors codes
- added some more descriptive error messages when fw returns invalid ranges
- removed unneeded explicit devm_regulator_unregister from .remove()
Link: https://lore.kernel.org/r/20201123202336.46701-4-cristian.marussi@arm.com

Signed-off-by: Mark Brown <broonie@kernel.org>