clk: rockchip: Support MMC clocks in GRF region

Registers of MMC drive/sample clocks in Rockchip RV1106 and RK3528
locate in GRF regions. Adjust MMC clock code to support register
operations through regmap.

Signed-off-by: Yao Zi <ziyao@disroot.org>
Link: https://lore.kernel.org/r/20250506092206.46143-3-ziyao@disroot.org


Signed-off-by: Heiko Stuebner <heiko@sntech.de>