clk: renesas: rzg2l: Refactor SD mux driver

Refactor SD MUX driver to be able to reuse the same code on RZ/G3S.
RZ/G2{L,UL} has a limitation with regards to switching the clock source
for SD MUX (MUX clock source has to be switched to 266MHz before
switching b/w 533MHz and 400MHz).  Rework the handling of this limitation
to use a clock notifier that is registered according to platform based
initialization data, so the SD MUX code can be reused on RZ/G3S.

As RZ/G2{L,UL} and RZ/G3S use different bits in different registers to
check if the clock switching has been done, this configuration (register
offset, register bits and bitfield width) is now passed through struct
cpg_core_clk::sconf (status configuration) from platform specific
initialization code.

Along with struct cpg_core_clk::sconf the mux table indices are also
passed from platform specific initialization code.

Also, mux flags are now passed to DEF_SD_MUX() as they will be used
later by RZ/G3S.

CPG_WEN_BIT macro has been introduced to select properly the WEN bit
of various registers.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231006103959.197485-3-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>