ARM: dts: renesas: Add interrupt-names to arch timer nodes

Add interrupt-names properties to device nodes that represent ARM
architected timers for clarity.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/b964e2f916cc23b6272e158c7b24597c971a82a5.1718890849.git.geert+renesas@glider.be