Add four tests for read and write performance per
different transfer size, 4k to 4M.
 * Read using blocking mmc request
 * Read using non-blocking mmc request
 * Write using blocking mmc request
 * Write using non-blocking mmc request

The host driver must support pre_req() and post_req()
in order to run the non-blocking test cases.
Signed-off-by: NPer Forlin <per.forlin@linaro.org>
Acked-by: NKyungmin Park <kyungmin.park@samsung.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NVenkatraman S <svenkatr@ti.com>
Tested-by: Sourav Poddar<sourav.poddar@ti.com>
Tested-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NChris Ball <cjb@laptop.org>