dt-bindings: nand: meson: add support for more SoCs

Older Amlogic SoCs have a slightly different integration of the NFC
(NAND flash controller) than the new ones (GXL, GXM, AXG).

On GXL, AXG and newer the "NAND device clock" is shared with sd_emmc_c.
This requires muxing the signal of that clock between the sd_emmc_c
controller and the NAND controller. The "amlogic,mmc-syscon" property
exists for this purpose.

Older SoCs (Meson8, Meson8b, Meson8m2 and GXBB) have a dedicated "NAND
device clock". Thus we don't need to "amlogic,mmc-syscon" property for
muxing the clock on these older SoCs.

The clock implementation itself is also more advanced on newer SoCs
because the phase of the RX and TX clock can be controlled. Older SoCs
cannot change the phase of the "NAND device clock". Thus the "rx" and
"tx" clock-names are only required for the GXL, GXM and AXG SoCs.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>