refactor(dt-bindings): align irq bindings with kernel

The arm-gic.h was a concatenation of arm-gic.h and irq.h from Linux.
Just copy the 2 files here. They both have MIT license which is accepted
in TF-A.
With this alignment, a new macro is added (GIC_CPU_MASK_SIMPLE).

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: Ib45174f35f1796ebb7f34af861b59810cfb808b0
diff --git a/docs/license.rst b/docs/license.rst
index f0caa39..80f1118 100644
--- a/docs/license.rst
+++ b/docs/license.rst
@@ -81,6 +81,7 @@
    terms of the MIT license. These files are:
 
    -  ``include/dt-bindings/interrupt-controller/arm-gic.h``
+   -  ``include/dt-bindings/interrupt-controller/irq.h``
 
    See the original `Linux MIT license`_.