mmc: Allow host drivers to specify a max block size

Most controllers have an upper limit on the block size. Allow the host
drivers to specify this and make sure we avoid hitting this limit.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/drivers/mmc/at91_mci.c b/drivers/mmc/at91_mci.c
index aa152f3..e28850d 100644
--- a/drivers/mmc/at91_mci.c
+++ b/drivers/mmc/at91_mci.c
@@ -823,6 +823,8 @@
 	mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
 	mmc->caps = MMC_CAP_BYTEBLOCK;
 
+	mmc->max_blk_size = 4095;
+
 	host = mmc_priv(mmc);
 	host->mmc = mmc;
 	host->buffer = NULL;