mmc: card: Add explicit checks for secure-discard requests

Discard request is no more overloaded with secure discard operation on
latest kernels. This change was introduced with commit "288dab8a".
Earlier, it was issued as discard request.

We have a check for not to fetch a new DCMD request (flush/discard) if
mmc driver is already processing a DCDM request. But since here
secure-erase request which also a DCMD request getting issued as a
separate request (i.e., not as discard request), its getting issued and
mmc driver is trying to process another DCMD while a DCMD is already in
progress which can mess-up the command queue h/w & s/w state machines.

Adding explicit checks for secure-discard request besides discard
request in the cmdq request issueing path. This would ensure that
secure discard request won't get fetched while another DCDM is active.

Change-Id: Ie0e8fdd44fc6fb2e1bb3b7c595ef32b66128ac5f
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>