riscv: defconfig : add CONFIG_MMC_DW for starfive

If these config not set, mmc can't run for jh7110, rootfs can't
be found when using SD card. So set CONFIG_MMC_DW=y like arm64
defconfig, and set CONFIG_MMC_DW_STARFIVE=y for starfive. Then
starfive vf2 board can start SD card rootfs with mainline defconfig
and dtb.

Signed-off-by: Jinyu Tang <tangjinyu@tinylab.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230912133128.5247-1-tangjinyu@tinylab.org


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>