mmc: core: Fix debugfs and IOCTL calls in cmdq mode

Currently getting status/ext_csd using debugfs or IOCTL
calls in cmdq mode is not working.
Fix it by halting the cmdq engine and making sure that
card queue is empty before issuing these cmds.

Change-Id: Idb89def9ff5c2fee6866759b9a8c652049552933
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>