vulkan-samples: limit to aarch64/x86-64

This package is only tested upstream for aarch64 and x86-64 targets,
for example there are int/long cast issues on 32-bit platforms and ATSC
is only ported to aarch64/x86-64.

Instead of listing the machines where we know it doesn't work, limit the
recipe to machines where it is known to work.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>