debian/control: add loong64 support

Dear Maintainers,

I have added support for the "loong64" architecture in the debian/control file of the mmseqs2 software package. The updated Architecture field now includes "loong64" along with other architectures:

Architecture: amd64 arm64 mips64el ppc64el ia64 kfreebsd-amd64 riscv64 loong64

Thank you for your attention to this update.