utils: add ARM64 to supported host architectures
utils: add ARM64 to supported host architectures

In order to support building on arm64 hosts (such as apple silicon), let's
update our uname parsing code to resolve the 'arm64' architecture to
Architecture.ARM64 instead of Architecture.ARM.

Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/691>

nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero