xen/arm: move a few DT related defines to public/device_tree_defs.h

xen/arm: move a few DT related defines to public/device_tree_defs.h

Move a few constants defined by libxl_arm.c to
xen/include/public/device_tree_defs.h, so that they can be used from Xen
and libxl. Prepend GUEST_ to avoid conflicts.

Move the DT_IRQ_TYPE* definitions from libxl_arm.c to
public/device_tree_defs.h. Use them in Xen where appropriate.

Re-define the existing Xen internal IRQ_TYPEs as DT_IRQ_TYPEs: they
already happen to be the same, let make it clear.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
CC: ian.jackson@eu.citrix.com