clk: renesas: r8a7795: Add CR clock

Add the CR core clock, which is used by the Secure Engine (SCEG).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Tested-by: Gilad Ben-Yossef <gilad@benyossef.com>