ARM: dts: aspeed-g6: Add SGPIO node.

AST2600 supports 2 SGPIO master interfaces one with 128 pins another one
with 80 pins.

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>
Link: https://lore.kernel.org/r/20210712100317.23298-4-steven_lee@aspeedtech.com


Signed-off-by: Joel Stanley <joel@jms.id.au>