[ARM] Exynos4: remove unwanted OdroidX defintion.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[ARM] Exynos4: Add Odroid support

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DOCS] Add OdroidX doxumentation.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>