xsm: Switch xsm_ops to __alt_call_maybe_initdata

xsm: Switch xsm_ops to __alt_call_maybe_initdata

This should have been done at the point xsm_ops became fully altcall'd.  This
puts the xsm_ops structure in .init on architectures where it is no longer
referenced at runtime.

Fixes: d868feb95a8a ("xen/xsm: Complete altcall conversion of xsm interface")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>