drm/exynos: added validation of edid for vidi connection

If edid of vidi from user is invalid, size calculated from a number
of cea extensions can be wrong. So, validation should be checked.

Changelog v2:
- just code cleanup
  . declare raw_edid only if vidi->connection is enabled.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>