xen/dt: reject "xen,static-mem" when CONFIG_STATIC_MEMORY is disabled

process_domain_node() parses "xen,static-mem" regardless of
CONFIG_STATIC_MEMORY. With the feature off, init_staticmem_pages() is a
no-op stub, so boot carries on until construct_domU() reaches the
ASSERT_UNREACHABLE() stubs of allocate_static_memory() /
assign_static_memory_11(): a debug build trips the assertion, a production
build gives the domain no memory at all.

Bail out at parse time instead, like process_shm_node() already does for
CONFIG_STATIC_SHM.

Fixes: 41c031ff43 ("xen/arm: introduce domain on Static Allocation")
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Bertrand Marquis <bertrand.marquis@arm.com>
[michal: adjust for code movement]
(cherry picked from commit e888192d13)

xen/common/device-tree/bootfdt.c

@@ -471,6 +471,12 @@ static int __init process_domain_node(const void *fdt, int node,
         /* No "xen,static-mem" present. */
         return 0;
 
+    if ( !IS_ENABLED(CONFIG_STATIC_MEMORY) )
+    {
+        printk("CONFIG_STATIC_MEMORY must be enabled for parsing xen,static-mem\n");
+        return -EINVAL;
+    }
+
     return device_tree_get_meminfo(fdt, node, "xen,static-mem", address_cells,
                                    size_cells, bootinfo_get_reserved_mem(),
                                    MEMBANK_STATIC_DOMAIN);