I think the SAMA5D2 has a different MMC controller from the D3 and D4. The D2 has SDMMC, I think the D3 and D4 have HSMCI. There's code in the Atmel software package repo for both, but SDMMC I couldn't find it in NuttX.
You would have to compare the register offsets and bit definitions to know if the underlying is the same or not. There are other drivers of *_sdmmc.c, you might check but the chances of that being the same IP would be pretty low (but I have been surprised in the past).
