mmc: sdhci-msm: Ensure larger discard size

Discard size calculation uses max_busy_timeout in deriving the
value. So, we can ensure a larger discard size by setting this
timeout as zero. If this timeout is zero then it takes max erase
timeout vlaue (which is 60sec) in the discard size calculation.

And qcom SDHC can support h/w based busy detection, So
we need set MMC_CAP_NEED_RSP_BUSY capability flag.

Since Qcom SDHC can support h/w based busy detection for R1b
commands, this timeout value is not relevant for us.
Setting it zero won't affect in any operation provied
MMC_CAP_NEED_RSP_BUSY cap is set.

Change-Id: Ib20a1e536d2e24cf8de1e927715a8a3aa7f0ae27
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>