ARM: shmobile: sh73a0: Remove global GPIO_NR definition

The total number of SoC GPIOs is only used to compute the base GPIO
number of th PCF8575 GPIO extender on the KZM9G board. As GPIO
allocation became fully dynamic with DT, no other SH73A0 board will use
the GPIO_NR macro. Move it to the KZM9G board file.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>