Fix the following sparse warnings:

arch/arm/mach-imx/gpc.c:29:6: warning: symbol 'imx_gpc_pre_suspend' was not declared. Should it be static?
arch/arm/mach-imx/gpc.c:43:6: warning: symbol 'imx_gpc_post_resume' was not declared. Should it be static?
arch/arm/mach-imx/gpc.c:71:6: warning: symbol 'imx_gpc_mask_all' was not declared. Should it be static?
arch/arm/mach-imx/gpc.c:83:6: warning: symbol 'imx_gpc_restore_all' was not declared. Should it be static?
arch/arm/mach-imx/gpc.c:122:13: warning: symbol 'imx_gpc_init' was not declared. Should it be static?
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>