For HDMI and LVDS display you can set mmcargs using u-boot setenv command.
HDMI
setenv displayinfo 'video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24'
setenv mmcargs ${mmcargs} video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24
LVDS
setenv displayinfo 'video=mxcfb0:dev=ldb,if=RGB666'
setenv mmcargs ${mmcargs} video=mxcfb0:dev=ldb,if=RGB666
For different display you can refer Specifying display section from section 4.7 Running Linux OS on the target of i.MX Linux User's guide as per below.
Regards
Radhika Somaiya.