mmc: core: allow hosts to specify a large discard size

max_busy_timeout is used to decide whether R1B response should
be used or a R1 response should be used. This is also used to
decide what the discard size of mmc queue (registered with block
layer) can be set to. In order to keep both the features in place,
this change will allow for hosts to specify a larger discard size
while still specifying max_busy_timeout.

Change-Id: I4f92ecc8afe6614019da5f5e51c37ceca85af819
Signed-off-by: Ziqi Chen <ziqichen@codeaurora.org>
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>