clk: shmobile: r8a7795: Add FCP clocks

The parent clock isn't documented in the datasheet, use S2D1 as a best
guess for now.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>