rockchip: rk3588: Add support for sdmmc clocks in SPL

Booting from sdmmc on RK3588 currently works because of a workaround in
the device tree, clocks are reordered so that the driver use ciu-sample
instead of ciu, and the BootRom initializes sdmmc clocks before SPL is
loaded into DRAM.

The sdmmc clocks are normally controlled by TF-A using SCMI. However,
there is a need to control these clocks in SPL, before TF-A has started.

This adds a rk3588_scru driver to control the sdmmc clocks in SPL before
TF-A has started, using scru regs. It also adds a small glue driver to
bind the scmi clock node to the rk3588_scru driver in SPL.

Fixes: 7a474df7 ("clk: rockchip: Add rk3588 clk support")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>