uboot-imx

common: Add a prototype for s_init()

When compiling with W=1 the following warning is observed:

arch/arm/mach-imx/mx6/soc.c:590:6: warning: no previous prototype for ‘s_init’ [-Wmissing-prototypes] void s_init(void)

Remove this warning by adding the function prototype into include/common.h file.

Signed-off-by: Diego Dorta <diego.dorta@nxp.com>