drivers: synopsys: Fix synopsys MMC driver

drivers: synopsys: Fix synopsys MMC driver

There are some issues with synopsys MMC driver:
- CMD8 should not expect data (for SD)
- ACMD51 should expect data (Send SCR for SD)
- dw_prepare should not dictate size to be MMC_BLOCK_SIZE, block size is
now handled in the dw_prepare function
- after the CMD completes, when doing dw_read, we need to invalidate cache
and wait for the data transfer to complete
- Need to set FIFO threshold, otherwise DMA might never get the interrupt
to read or write

Signed-off-by: Tien Hock, Loh <tien.hock.loh@intel.com>