clk: renesas: r8a7796: Add OSC EXTAL predivider configuration

R-Car Gen3 Hardware Manual Rev.0.52 documents the relation between the
MD13 and MD14 mode pins, and the OSC EXTAL predivider, as used by the
OSC and RINT RCLK clocks.  Hence augment the configuration structure
with all documented predivider values.

According to R-Car Gen3 Hardware Manual Rev.0.53, the CPG_RCKCR
register was removed in R-Car M3-W ES1.1.  Change the OSC and RINT
clock definitions to use the OSC EXTAL predivider instead, which is
supported on all R-Car M3-W SoC revisions.

Inspired by a patch in the BSP by Takeshi Kihara
<takeshi.kihara.df@renesas.com>.

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