phy: samsung-ufs: switch back to syscon_regmap_lookup_by_phandle()

phy: samsung-ufs: switch back to syscon_regmap_lookup_by_phandle()

Now exynos-pmu can register its custom regmap for gs101 via
of_syscon_register_regmap() we can switch back to the standard
syscon_regmap_lookup_by_phandle() api for obtaining the regmap.

Additionally add a Kconfig dependency for MFD_SYSCON.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20241029192107.2344279-1-peter.griffin@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>