IXP4xx: Fix Goramo Multilink GPIO conversion.

Commit 098e30f6558f8 "ARM: ixp4xx: stop broadcasting the custom GPIO API"
changed the internal gpio code of ixp4xx to be accessible only from
common.c, but unfortunately that broke the Goramo MultiLink code, which
uses this API.

arch/arm/mach-ixp4xx/goramo_mlr.c: In function 'set_scl':
arch/arm/mach-ixp4xx/goramo_mlr.c:82: error: implicit declaration of function 'gpio_line_set'

arch/arm/mach-ixp4xx/goramo_mlr.c: In function 'output_control':
arch/arm/mach-ixp4xx/goramo_mlr.c:111: error: implicit declaration of function 'gpio_line_config'
arch/arm/mach-ixp4xx/goramo_mlr.c:111: error: 'IXP4XX_GPIO_OUT' undeclared

arch/arm/mach-ixp4xx/goramo_mlr.c: In function 'hss_dcd_irq':
arch/arm/mach-ixp4xx/goramo_mlr.c:155: error: implicit declaration of function 'gpio_line_get'

arch/arm/mach-ixp4xx/goramo_mlr.c: In function 'gmlr_init':
arch/arm/mach-ixp4xx/goramo_mlr.c:416: error: 'IXP4XX_GPIO_OUT' undeclared
arch/arm/mach-ixp4xx/goramo_mlr.c:421: error: 'IXP4XX_GPIO_IN' undeclared

Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>