qt webkit: add support for MIPS64 platforms

qt5webkit is not fixed and this patch cannont be applied to qt5webkit

Task-number: QTBUG-35394

Change-Id: Ie2d332345741989a0b4ef93306ca36b42e888c11
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>