kmscon: add cairo-renderer module

kmscon: add cairo-renderer module

The cairo text renderer uses the cairo blitting functions to blit all
glyphs into the cairo-surface. This is only for testing-purposes. Cairo is
not really suited for blending/blitting of large surfaces. Hence, this
backend is horribly slow compared to bblit/bbulk.

This backend is disabled by default.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>