mips: do not list individual devices from configs/

mips: do not list individual devices from configs/

Add new "select" and "imply" directives if needed.  The resulting
config-devices.mak files are the same as before.
Builds without default devices will become much smaller
than before, and qtests fail (as expected, though suboptimal)
for mips64-softmmu because most tests do not use -nodefaults,
so remove it from build-without-defaults

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>