qt: webkit is now supported on MIPS64

Since qt's version has been bumped to 4.8.6 we can add support for
webkit on MIPS64 architectures (both big and little endian). It wasn't
possible on 4.8.5 because QtScript wasn't supported on MIPS64, but that
has been fixed on 4.8.6.

With reference to:
   https://codereview.qt-project.org/#change,73022



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Markos Chandras <Markos.Chandras@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>