qapi: Make some ObjectTypes depend on the build settings

qapi: Make some ObjectTypes depend on the build settings

Some of the ObjectType entries already depend on CONFIG_* switches.
Some others also only make sense with certain configurations, but
are currently always listed in the ObjectType enum. Let's make them
depend on the correpsonding CONFIG_* switches, too, so that upper
layers (like libvirt) have a better way to determine which features
are available in QEMU.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210928160232.432980-1-thuth@redhat.com>
[Do the same for MemoryBackendEpcProperties. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>