clk: renesas: Update R-Car Gen3 driver Gen4 support

clk: renesas: Update R-Car Gen3 driver Gen4 support

Update R-Car Gen4 support in Gen3 clock driver. This patch renames the
V3U clock parts to Gen4 and extends them by new PLL2, PLL3, PLL4, PLL6
as well as SDSRC clock which use undocumented bits so far, and RPCSRC
clock which uses its own more capable divider table. The Gen4 module
standby and reset tables are also updated.

This patch makes use of union to alias Gen3 and more extensive Gen4
PLL tables, as the driver cannot ever be instantiated on hardware
that would identify itself as both Gen3 and Gen4.

The V3U clock driver is updated to match Gen4 clock driver behavior,
it is augmented with a more extensive PLL table and a valid MODEMR
register offset.

This supersedes "clk: renesas: Introduce R-Car Gen4 CPG driver"
from Hai Pham as the R-Car Gen3 and Gen4 clock core drivers are
extremely similar. That implementation was in turn based on Linux
commit 470e3f0d0b15 ("clk: renesas: rcar-gen4: Introduce R-Car Gen4 CPG driver")
by Yoshihiro Shimoda .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>