gpio: aspeed: fix ast2600 bank properties

GPIO_U is mapped to the least significant byte of input/output mask, and
the byte in "output" mask should be 0 because GPIO_U is input only. All
the other bits need to be 1 because GPIO_V/W/X support both input and
output modes.

Similarly, GPIO_Y/Z are mapped to the 2 least significant bytes, and the
according bits need to be 1 because GPIO_Y/Z support both input and
output modes.

Fixes: ab4a8553 ("gpio: aspeed: Add in ast2600 details to Aspeed driver")
Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>