ARM: dts: fix Moxa SDIO 'compatible', remove 'sdhci' misnomer

Driver moxart-mmc.c has .compatible = "moxa,moxart-mmc".

But moxart .dts/.dtsi and the documentation file moxa,moxart-dma.txt
contain compatible = "moxa,moxart-sdhci".

Change moxart .dts/.dtsi files and moxa,moxart-dma.txt to match the driver.

Replace 'sdhci' with 'mmc' in names too, since SDHCI is a different
controller from FTSDC010.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Link: https://lore.kernel.org/r/20220907175341.1477383-1-saproj@gmail.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>