All of universal-obj-y, user-obj-y (right now unused) and common-obj-y can
be unified into common-obj-y if we take care of defining CONFIG_SOFTMMU
and CONFIG_USER_ONLY in the toplevel makefile.  This is similar to how
we define symbols for hardware components.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>