ARM: dts: r8a7790: Add missing clocks for secondary CA15 CPU cores

Currently only the primary CPU in the CA15 cluster has a clocks
property, while the secondary CPU cores are driven by the same clock.
Add the missing clocks properties to fix this.

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