[doxygen] Do not scan the whole source tree
[doxygen] Do not scan the whole source tree

Doxygen is rather verbose and scanning .git subdirectory produces a
lot of noise.

Limit scanning only to to subdirectories that have data for doxygen.

Signed-off-by: Simo Piiroinen <6d5e5360bed3d486f7d9fb26b0f737f7d4fd45ee@jollamobile.com>

spiiroin/mce-dev,spiiroin/mce-dev