soc: samsung: exynos-pmu: update to use of_syscon_register_regmap()

For SoCs like gs101 that need a special regmap, register this with
of_syscon_register_regmap api, so it can be returned by
syscon_regmap_lookup_by_phandle() and friends.

For SoCs that don't require a custom regmap, revert back to syscon
creating the mmio regmap rather than duplicating the logic here.

exynos_get_pmu_regmap_by_phandle() api is also updated to retrieve
the regmap via syscon. The exynos_get_pmu_regmap_by_phandle() api
is kept around until fw_devlink support for syscon property is added
for the pinctrl-samsung driver that also runs at postcore_initcall
level.

All other exynos client drivers can revert back to
syscon_regmap_lookup_by_phandle().

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Tested-by: Will McVicker <willmcvicker@google.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240621115544.1655458-3-peter.griffin@linaro.org


Signed-off-by: Lee Jones <lee@kernel.org>