soc: microchip_mec: mec1501: Fixup GPIO dts defines

Use address based defines in the dts_fixup.h instead of DT_INST_ based
ones.  The DT_INST_ will not get us the consistent mapping that is
needed (as we should assume the order of DT_INST_).

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>