mfd: sec: Add support for S2MPU05 PMIC

Add support for Samsung's S2MPU05 PMIC. It's the primary PMIC used by
Exynos7870 devices. It houses regulators (21 LDOs and 5 BUCKs) and a RTC
clock device.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250301-exynos7870-pmic-regulators-v3-2-808d0b47a564@disroot.org


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