arm64: a37xx: dts: Fix the number of GPIO on south bridge

arm64: a37xx: dts: Fix the number of GPIO on south bridge

The number of pins in South Bridge is 30 and not 29. There is a fix for
the driver for the pinctrl, but a fix is also need at device tree level
for the GPIO.

Reviewed-on: http://vgitil04.il.marvell.com:8080/43286
Reviewed-by: Hua Jing <jinghua@marvell.com>
Tested-by: iSoC Platform CI <ykjenk@marvell.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Ken Ma <make@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>