Enable CRC check on cmd/data responses

[enjoy-digital]

CRC check on responses has been disabled as part of #7. We need to understand why this was needed and only disable it on the commands that are not returning a CRC.

[paulusmack]

Response types R2 and R3 don't contain a CRC, so commands 2, 9, 10 and app cmd 41 won't have a CRC in the response.

The Linux MMC layer uses the MMC_RSP_CRC bit in cmd->flags to indicate whether the response has a CRC, so the low-level driver doesn't need to know.

I'll have a look at adding a bit to the CMDCMD register to indicate whether the response CRC should be checked.