media: platform: remove blackfin capture driver

The blackfin architecture is getting removed, so the video
capture driver is also obsolete.

Acked-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Aaron Wu <aaron.wu@analog.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>