xen/arm: Initialize trace buffer

Now that we allow a privileged domain to map tracing buffer, initialize
them so a user can effectively trace Xen.

Signed-off-by: Benjamin Sanda <ben.sanda@dornerworks.com>
[julien: rework commit message]
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/setup.c

@@ -36,6 +36,7 @@
 #include <xen/pfn.h>
 #include <xen/virtual_region.h>
 #include <xen/vmap.h>
+#include <xen/trace.h>
 #include <xen/libfdt/libfdt.h>
 #include <xen/acpi.h>
 #include <asm/alternative.h>
@@ -899,6 +900,8 @@ void __init start_xen(unsigned long boot_phys_offset,
 
     heap_init_late();
 
+    init_trace_bufs();
+
     init_constructors();
 
     console_endboot();