dt-bindings: nand: meson: fix meson nfc clock

EMMC and NAND have the same clock control register named 'SD_EMMC_CLOCK'
which is defined in EMMC port internally. bit0~5 of 'SD_EMMC_CLOCK' is
the divider and bit6~7 is the mux for fix pll and xtal. At the beginning,
a common MMC and NAND sub-clock was discussed and planed to be implemented
as NFC clock provider, but now this series of patches of a common MMC and
NAND sub-clock are never being accepted and the current binding was never
valid. the reasons for giving up are:
1. EMMC and NAND, which are mutually exclusive anyway
2. coupling the EMMC and NAND.
3. it seems that a common MMC and NAND sub-clock is over engineered.
and let us see the link fot more information:
https://lore.kernel.org/all/20220121074508.42168-5-liang.yang@amlogic.com
so The meson nfc can't work now, let us rework the clock.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Liang Yang <liang.yang@amlogic.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220907080405.28240-2-liang.yang@amlogic.com