mmc: sdhci-iproc: Increase max_blk_size for bcm2835

According to the BCM2835 datasheet the maximum block size for the
eMMC module is restricted to the internal data FIFO which is 1024 byte.
But this is still an improvement to the default of 512 byte.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>