riscv: dts: starfive: jh7110: Add DVP and HDMI TX pixel external clocks

Add DVP and HDMI TX pixel external fixed clocks and the rates are
74.25MHz and 297MHz.

Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Xingyu Wu <xingyu.wu@starfivetech.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>