x86/xen: Remove undefined behavior in setup_features()

[ Upstream commit ecb6237f ]

1 << 31 is undefined. So switch to 1U << 31.

Fixes: 5ead97c8

 ("xen: Core Xen implementation")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220617103037.57828-1-julien@xen.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>