Arch variable is ignored in UI meta packages

Since Phosh currently doesn't work on anything other than x86 and x86_64, the arch for the UI meta package is set to noarch !armhf !armv7 !aarch64. However, when picking any device that is not x86 or x86_64, pmbootstrap still shows Phosh as an option for the UI even though it will not build or work.

It should parse the actual arches that the package is available on, check if one of those arches is the one used by the device, and if not hide it from the list.