board: ge: bx50v3: Pass video bootargs for b850v3

Due to clock source restrictions on i.MX6, certain pixel clock rates can
not be supported. Hence default the resolution/frame rate during boot to a
supported value by passing video bootargs 1024x768@60 for
HDMI (Display Port1) and LVDS (Display Port2) on B850v3.

Signed-off-by: Ken Lin <ken.lin@advantech.com.tw>
Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>