configs: Enable Anbox support on arm64 builds

In order to allow containerised Android apps to run, add the following
config settings on 64-bit builds:

 CONFIG_ANDROID=y
 CONFIG_ANDROID_BINDER_IPC=y
 CONFIG_ANDROID_BINDERFS=y
 CONFIG_ASHMEM=y

This has a memory overhead of about 130kB and no other performance
penalty.

See: https://github.com/raspberrypi/linux/issues/4162

Signed-off-by: Phil Elwell <phil@raspberrypi.com>