genirq: Document interaction between <linux/irq.h> and DT binding defines

genirq: Document interaction between <linux/irq.h> and DT binding defines

Document that the DT binding definitions in
<dt-bindings/interrupt-controller/irq.h> shadow the first six IRQ_TYPE_*
definitions in <linux/irq.h>.  The values must be the same anyway, so this
is harmless (as long as the latter is included first when both are
included), but it is good to document this explicitly.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/fbcc65dcee6c5437fab5ef18d21766bb4effb7cb.1772644406.git.geert+renesas@glider.be