imx8qxp_mek: Include fdt_support.h header

Include fdt_support.h header file to fix the following sparse warning:

board/freescale/imx8qxp_mek/imx8qxp_mek.c:129:5: warning: no previous
prototype for ‘ft_board_setup’ [-Wmissing-prototypes]

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