intr: Further delay MachIntrABI.finalize()

intr: Further delay MachIntrABI.finalize()

It only affects SMP case.  For ICU, it will be better if finalize()
is called after IMCR detection is done, though on most modern systems
IMCR does not exist.  For I/O APIC, finalize() _should_ be called
after BSP's LAPIC is initialized, since it alters BSP LAPIC's LINT0
and LINT1 configuration.

Add stabilize() ABI to MachIntrABI which is only implemented by ICU
currently and this ABI is called in the place where finalize() used
to be called.