imx8mm_evk: Include sys_proto.h header

Add sys_proto.h header file to fix the following sparse warning:

board/freescale/imx8mm_evk/imx8mm_evk.c:59:5: warning: no previous
prototype for ‘board_mmc_get_env_dev’ [-Wmissing-prototypes]

Signed-off-by: Alifer Moraes <alifer.wsdm@gmail.com>
1 file changed