- Rename subpackage vaapi-drivers -> vaapi-dummy-driver
since dummy is the only driver this package contains.
- Let the library recommend the dummy driver in case no other
is present

- Remove intel-driver, it has been packaged separately
with proper hardware "Supplements" so it gets installed
only when needed.
- Fix -devel package requires, otherwise dependant packages
fail with missing headers wanted by files in /usr/include/va.