x86/xen/pvh: Annotate indirect branch as safe

[ Upstream commit 82694854caa8badab7c5d3a19c0139e8b471b1d3 ]

This indirect jump is harmless; annotate it to keep objtool's retpoline
validation happy.

Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/4797c72a258b26e06741c58ccd4a75c42db39c1d.1611263462.git.jpoimboe@redhat.com


Stable-dep-of: e8fbc0d9cab6 ("x86/pvh: Call C code via the kernel virtual mapping")
Signed-off-by: Sasha Levin <sashal@kernel.org>