mmc: dw_mmc: fix fifo ordering in big endian

The dw_mmc driver changes to make the IO accesors endian agnostic did not
take into account the fifo accesses do not need to be swapped. To fix this
add a mmci_fifo_read/write wrapper to allow these to be passed through the
IO without being swapped.

Since these are now specific functions, it would be easier just to store
the pointer to the fifo registers in the host block instead of the offset
to them. So change the host->data_offset to host->fifo_reg (which also
means we catch all the places this is read or written).

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>