imx: 8qxp_mek: fix fdt_file and console

Fix fdt_file and console to boot upstream Linux Kernel.

Upstream linux use imx8qxp-mek.dtb, and pass lpuart32 to earlycon
will not work for i.MX8QXP, only need to pass earlycon,
check drivers/tty/serial/earlycon.c,
" /* Just 'earlycon' is a valid param for devicetree and ACPI SPCR. */ "

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>