Use binfmt-support --fix-binary option (#868030)

binfmt-support 2.1.7 added the --fix-binary boolean option that maps to
the kernel's F binfmt flag[1]. This flag instructs the kernel to open
the binfmt handler immediately when registered. This is very helpful in
the case of qemu-user-static where emulation of another architecture can
be handled with no updates to a chroot or container running foreign
architecture binaries.

However, in the case of qemu-user and qemu-update-binfmt, this is less
likely to be helpful since dynamic linking would still require the many
libraries in the alternate root. In that case, continue to run
update-binfmts without --fix-binary.

1. https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html