Add default configuration for the AArch64 Foundation V8 simulator

Note that this configuration doesn't build entirely: the user must
manually run "make busybox-menuconfig" and disable the "Mount NFS
filesystems" option, because the toolchain does not have RPC support.

This issue will be fixed once the support for toolchain without RPC
will be integrated.

[Peter: fix readme typo]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>