vfio: selftests: only build tests on arm64 and x86_64

vfio: selftests: only build tests on arm64 and x86_64

Only build vfio self-tests on arm64 and x86_64; these are the only
architectures where the vfio self-tests are run. Addresses compiler
warnings for format and conversions on i386.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601211830.aBEjmEFD-lkp@intel.com/
Signed-off-by: Ted Logan <tedlogan@fb.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20260202-vfio-selftest-only-64bit-v2-1-9c3ebb37f0f4@fb.com
Signed-off-by: Alex Williamson <alex@shazbot.org>