riscv: defconfig: Enable mmc and dma drivers for T-Head TH1520

Enable the mmc controller driver and dma controller driver needed for
T-Head TH1520 based boards, like the LicheePi 4A and BeagleV-Ahead, to
boot from eMMC storage.

Reviewed-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20231206-th1520_mmc_dts-v8-1-69220e373e8f@baylibre.com


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