riscv: dts: starfive: Add JH7100 MMC nodes

Add device tree nodes for the Synopsis MMC controllers on the
StarFive JH7100 SoC.

Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>