arm64: dts: renesas: r8a779a0: Add missing hypervisor virtual timer IRQ

Add the missing fifth interrupt to the device node that represents the
ARM architected timer.  While at it, add an interrupt-names property for
clarity,

Fixes: 834c310f ("arm64: dts: renesas: Add Renesas R8A779A0 SoC support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/671416fb31e3992101c32fe7e46147fe4cd623ae.1718890849.git.geert+renesas@glider.be