clk: starfive: Add JH7100 clock generator driver

Add a driver for the StarFive JH7100 clock generator.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Co-developed-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>