x86/ibt,xen: Sprinkle the ENDBR

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2090231



commit 5b2fc515
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Tue, 8 Mar 2022 16:30:23 +0100

    x86/ibt,xen: Sprinkle the ENDBR

    Even though Xen currently doesn't advertise IBT, prepare for when it
    will eventually do so and sprinkle the ENDBR dust accordingly.

    Even though most of the entry points are IRET like, the CPL0
    Hypervisor can set WAIT-FOR-ENDBR and demand ENDBR at these sites.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lore.kernel.org/r/20220308154317.873919996@infradead.org



Signed-off-by: Waiman Long <longman@redhat.com>