The Synopsys DesignWare APB GPIO controller driver does not parse
reg-io-width and dtschema does not allow it so drop it to fix dtschema
warnings like:

  arch/arm/boot/dts/picoxcell-pc7302-pc3x2.dt.yaml: gpio@20000:
    'reg-io-width' does not match any of the regexes: '^gpio-(port|controller)@[0-9a-f]+$', 'pinctrl-[0-9]+'

Link: https://lore.kernel.org/r/20200917164909.22490-1-krzk@kernel.orgSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Olof Johansson <olof@lixom.net>