memory: notify hypervisor of all eventfds during listener (de)registration

memory: notify hypervisor of all eventfds during listener (de)registration

When a new listener for an address space is registered, the hypervisor must be
informed of all existing eventfds for that address space by calling
eventfd_add() for that listener. Similarly, when a listener is de-registered
from an address space, the hypervisor must be informed of all existing eventfds
for that address space with a call to eventfd_del().

Same is also true for coalesced io. Send coalesced io add/del listener
notifications if any flatrage for the address space registered with the
listener intersects with any coalesced io range.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Link: https://lore.kernel.org/r/20240918064853.30678-1-anisinha@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>