ENGR00251830 LDB: Fix the bug of LDB separate mode for dual LVDS display

ENGR00251830 LDB: Fix the bug of LDB separate mode for dual LVDS display

Fix the bug of LDB separate mode for dual LVDS display on i.mx6.
For 'ldb=sep0' option on kernel command line, it means that LVDS0 is
the primary display. While 'ldb=sep1' means that LVDS1 is the primary display.
For LDB separate mode, the Display Interface(disp_id) should be
configured differently on the platform layer. That is, IPU DI0 to LVDS1 or
IPU DI1 to LVDS0 configuration should be avoided.

Signed-off-by: Wayne Zou <b36644@freescale.com>