mmc: change mmc_delay() to use usleep_range()

Use the usleep_range() to simplify mmc_delay() and give some more
accuracy to it - but with an exception of mmc_card_sleepawake():
since sleep/awake timeout varies in a wide range, different
delay methods should be used.

Signed-off-by: Dmitry Antipov <dmitry.antipov@linaro.org>
Signed-off-by: nobodyAtall <tsogkas@ceid.upatras.gr>
Signed-off-by: garwedgess <garethwilliams21@gmail.com>