Add support for the mmc controller of Sophgo SG2042.

SG2042 uses Synopsys PHY the same as TH1520 so we reuse the tuning
logic from TH1520. Besides this, this patch implement some SG2042
specific work, such as clocks and reset ops.
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/eb21847528a6487af54bb80f1ce94adff289cdb0.1722847198.git.unicorn_wang@outlook.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>