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/au1xmmc.c b/drivers/mmc/au1xmmc.c
index 6d6fe6e..74e6ac0 100644
--- a/drivers/mmc/au1xmmc.c
+++ b/drivers/mmc/au1xmmc.c
@@ -922,6 +922,8 @@
 		mmc->max_seg_size = AU1XMMC_DESCRIPTOR_SIZE;
 		mmc->max_phys_segs = AU1XMMC_DESCRIPTOR_COUNT;
 
+		mmc->max_blk_size = 2048;
+
 		mmc->ocr_avail = AU1XMMC_OCR;
 
 		host = mmc_priv(mmc);