drm/exynos: set the active aspect ratio as per mode

Now that the drm_display_mode also provides aspect
ratio for all resolutions, this patch adds its usage
to set the active aspect ratio of AVI info frame
packets as per CEA-861-D standard's Table 9.

This is also needed to abide by the 7-27
compliance test of HDMI.

Signed-off-by: Shirish S <s.shirish@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>