dt-bindings: aspeed-sgpio: Add ast2600 sgpio

AST2600 SoC has 2 SGPIO master interfaces one with 128 pins another one
with 80 pins. Add ast2600-sgpiom compatibles and update descriptions to
introduce the max number of available gpio pins that AST2600 supported.

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210712100317.23298-3-steven_lee@aspeedtech.com


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