riscv: dts: starfive: Enable SD-card on JH7100 boards

Add pinctrl and MMC device tree nodes for the SD-card on the
BeagleV Starlight and StarFive VisionFive V1 boards.

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