imx: imx6: Move gpr_init() function to soc.c

Since the gpr_init() function is common for boards using MX6S, MX6DL, MX6D,
MX6Q and MX6QP processors move it to the soc.c file.

Signed-off-by: Breno Lima <breno.lima@nxp.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

arch/arm/include/asm/mach-imx/sys_proto.h

@@ -90,6 +90,8 @@ static inline u8 imx6_is_bmode_from_gpr9(void)
 }
 
 u32 imx6_src_get_boot_mode(void);
+void gpr_init(void);
+
 #endif /* CONFIG_MX6 */
 
 u32 get_nr_cpus(void);