ARM: dts: r8a7790: Correct mask for GIC PPI interrupts

R-Car H2 (r8a7790) contains four Cortex-A15 and four Cortex-A7 cores,
hence the second interrupt specifier cell for Private Peripheral
Interrupts should use "GIC_CPU_MASK_SIMPLE(8)", to make sure interrupts
can be delivered to all 8 processor cores.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>