ARM: dts: at91: sama7g5: Add NAND support

Add NAND support. The sama7g5's SMC IP is the same as sama5d2's with
a slightly change: it provides a synchronous clock output (SMC clock)
that is dedicated to FPGA usage. Since this doesn't interfere with the SMC
NAND configuration, thus code will not be added in the current nand driver
to address the FPGA usage, use the sama5d2's compatible and choose not to
introduce dedicated compatibles for sama7g5.
Tested with Micron MT29F4G08ABAEAWP NAND flash.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
[nicolas.ferre@microchip.com: add the definition of PMC_MCK1 in
	include/dt-bindings/clock/at91.h from another patch]
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220111130556.905978-1-tudor.ambarus@microchip.com