qt5base: Add support for MIPS64 BigEndian

This patch adds support for MIPS64 BigEndian platforms and has already
been merged upstream:

https://github.com/qtproject/qtbase/commit/cea101bd10cc158b97d5fbf45b33dad9b649c08b



Now we can remove the restriction on the Config.in to disable the
selection of this packages on MIPS64 BigEndian platforms.

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