clk: starfive: Add StarFive JH7110 PLL clock driver

Add driver for the StarFive JH7110 PLL clock controller
and they work by reading and setting syscon registers.

Co-developed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Xingyu Wu <xingyu.wu@starfivetech.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>