omap2/3/4: gpmc: kill compile warning

Get rid of the following warnings:

arch/arm/mach-omap2/gpmc.c:550:30: warning: non-ANSI
function declaration of function 'omap3_gpmc_save_context'

arch/arm/mach-omap2/gpmc.c:581:33: warning: non-ANSI
function declaration of function 'omap3_gpmc_restore_context'

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>