This change adds arm64/aarch64 images to supported distributions.
This is triggered if BUILD_MULTI_ARCH_IMAGE=true.
Note that for ubi8 images this means that we switch to using centos8
packages instead of centos7 since we do not build aarch64 packages
for the latter.
This also means that for centos7 we only build x86_64 images.
Signed-off-by: Evan Lezar <elezar@nvidia.com>
