xen/x86: add desc_equal() to compare GDT descriptors

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
[v1: Moving it to the Xen file]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 0c1ab43..225ffdc 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -539,6 +539,12 @@
 		BUG();
 }
 
+static inline bool desc_equal(const struct desc_struct *d1,
+			      const struct desc_struct *d2)
+{
+	return d1->a == d2->a && d1->b == d2->b;
+}
+
 static void load_TLS_descriptor(struct thread_struct *t,
 				unsigned int cpu, unsigned int i)
 {