imx: imx8qxp_mek: increase buffer sizes and args number

The default value of CONFIG_SYS_CBSIZE is too small when we need
to input long commands or when using long kernel command line.

The default value of CONFIG_SYS_MAXARGS is too small to add a long
command line, and the kernel might not boot as intended without the
complete bootargs. Increase argument buffer sizes and the number of
arguments.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>