buildroot

mesa3d: allow the VC4 driver to be selected on AArch64

Neon is compulsory on AArch64, and BR2_ARM_CPU_HAS_NEON is false on
AArch64. Therefore, this change is needed to enable building VC4
gallium driver for Rpi3 using AArch64.

Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>