soc: samsung: exynos-pmu: Add regmap support for SoCs that protect PMU regs

Some Exynos based SoCs like Tensor gs101 protect the PMU registers for
security hardening reasons so that they are only write accessible in el3
via an SMC call.

As most Exynos drivers that need to write PMU registers currently obtain a
regmap via syscon (phys, pinctrl, watchdog). Support for the above usecase
is implemented in this driver using a custom regmap similar to syscon to
handle the SMC call. Platforms that don't secure PMU registers, get a mmio
regmap like before. As regmaps abstract out the underlying register access
changes to the leaf drivers are minimal.

A new API exynos_get_pmu_regmap_by_phandle() is provided for leaf drivers
that currently use syscon_regmap_lookup_by_phandle(). This also handles
deferred probing.

Tested-by: Sam Protsenko <[email protected]>
Tested-by: Alexey Klimov <[email protected]>
Reviewed-by: Sam Protsenko <[email protected]>
Signed-off-by: Peter Griffin <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Krzysztof Kozlowski <[email protected]>

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