dt-bindings: pinctrl: spacemit: fix drive-strength check warning

dt-bindings: pinctrl: spacemit: fix drive-strength check warning

The problem is that one value from drive-strength may match to more than
two different enum groups which lead to DT complaint, switch to use 'anyOf'
to fix this kind warning.

Fixes: c3efac0592f8 ("dt-bindings: pinctrl: spacemit: convert drive strength to schema format")
Signed-off-by: Yixun Lan <dlan@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>