builddeb: fix cross-building to arm64 producing host-arch debs

builddeb: fix cross-building to arm64 producing host-arch debs

commit 152b695d74376bfe55cd2a6265ccc75b0d39dd19 upstream.

Both Debian and kernel archs are "arm64" but UTS_MACHINE and gcc say
"aarch64".  Recognizing just the latter should be enough but let's
accept both in case something regresses again or an user sets
UTS_MACHINE=arm64.

Regressed in cfa88c7: arm64: Set UTS_MACHINE in the Makefile.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Acked-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Michal Marek <mmarek@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>