gk802: Remove board support

The gk802 is not being actively maintained at this moment and it lacks
support for current GPU version.

This patch remove the board and specific recipes and can be reverted
later when a better support is provided for this board.

Change-Id: I0575c244945d7b4ee78ac47aae5c4a5d0bfbd793
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>