dt-bindings: mmc: sdhci-of-dwcmhsc: Add Sophgo SG2042 support

SG2042 use Synopsys dwcnshc IP for SD/eMMC controllers.

SG2042 defines 3 clocks for SD/eMMC controllers.
- EMMC_100M/SD_100M for cclk(Card clocks in DWC_mshc), so reuse
  existing "core".
- AXI_EMMC/AXI_SD for aclk/hclk(Bus interface clocks in DWC_mshc)
  and blck(Core Base Clock in DWC_mshc), these 3 clocks share one
  source, so reuse existing "bus".
- 100K_EMMC/100K_SD for cqetmclk(Timer clocks in DWC_mshc), so reuse
  existing "timer" which was added for rockchip specified.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/9ca450097e5389a38bcd7d8ddf863766df4cea10.1722847198.git.unicorn_wang@outlook.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>