pinctrl: aspeed: Allow changing SPI mode from hardware strap defaults

Some platforms unfortunately have their SPI mode selection bits
strapped incorrectly (such as being configured for passthrough mode
when master mode is in fact the only useful configuration for it) and
thus require correction in software.  Add the SPI mode bits to the
GPIO passthrough bits as the exceptions to the read-only rule for the
hardware strap register so that the pinctrl subsystem can be used for
such corrections.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20231005030849.11352-2-zev@bewilderbeest.net


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>