OMAP3: export enable_gpmc_cs_config to board files

Export enable_gpmc_cs_config into common header to
prevent warning:

warning: implicit declaration of function 'enable_gpmc_cs_config'

Signed-off-by: Nishanth Menon <nm@ti.com>

include/asm-arm/arch-omap3/sys_proto.h

@@ -34,6 +34,8 @@ void memif_init(void);
 void sdrc_init(void);
 void do_sdrc_init(u32, u32);
 void gpmc_init(void);
+void enable_gpmc_cs_config(u32 *gpmc_config, struct gpmc_cs *cs, u32 base,
+			u32 size);
 
 void watchdog_init(void);
 void set_muxconf_regs(void);