MAINTAINERS: Add qemu-binfmt-conf.sh script

qemu-binfmt-conf.sh is used for the Linux usermode emulation, so
let's add this file to that section in the MAINTAINERS file.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>