xen/mem_sharing: wrap hvm_copy_context_and_params() with CONFIG_MEM_SHARING

The only reference of hvm_copy_context_and_params() is in
arch/x86/mm/mem_sharing.c, so it shall be wrapped with CONFIG_MEM_SHARING.
Otherwise it will become unreachable when MEM_SHARING=n, and hence violating
Misra rule 2.1.

Signed-off-by: Penny Zheng <Penny.Zheng@amd.com>
Reviewed-by: Grygorii Strashko <grygorii_strashko@epam.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/hvm.c

@@ -5458,6 +5458,7 @@ void hvm_set_segment_register(struct vcpu *v, enum x86_segment seg,
     alternative_vcall(hvm_funcs.set_segment_register, v, seg, reg);
 }
 
+#ifdef CONFIG_MEM_SHARING
 int hvm_copy_context_and_params(struct domain *dst, struct domain *src)
 {
     struct hvm_domain_context c = { .size = hvm_save_size(src) };
@@ -5489,6 +5490,7 @@ int hvm_copy_context_and_params(struct domain *dst, struct domain *src)
 
     return rc;
 }
+#endif /* CONFIG_MEM_SHARING */
 
 /*
  * Local variables: