The kernel command line configuration for display may vary according the kernel release. You will find the correct parameters at release notes contained at the BSP package you're using. For example, for BSP release the video command line is: video=mxcfb0:dev=ldb,LDB-XGA,if=RGB666 video=mxcfb1:dev=hdmi, 1920x1080M@60,if=RGB24
If you switch the fb0 with fb1, Linux will switch the primary display. For example, if lcd was the /dev/fb0, it will now be the /dev/fb1. all this is done in uboot.