package/mali-driver: only available for arm or AArch64

Currentlym this kernel module can be built by any architecture and this
leads to many failures. Since it's very unlikely that Mali will be part
of architectures other than AArch64 and arm let's depend on BR2_aarch64
and BR2_arm only.

Fixes:
http://autobuild.buildroot.net/results/f94885ef76865c3888d6cc52b35c93a742f92f3a



Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>