Revert "scsi: sd: remove check_events callback"

This reverts commit fe64842c.
On auto platforms, it is observed that sdcard is not getting
detected using usb card reader as check_events callback was
removed. For usb card reader case, scsi check_events() callback
is required which sends test unit ready command to check if
underlying media state has changed. So instead of removing
check_events() completely, simply return for embedded storage
media like UFS.

Change-Id: Iefd163db1a1098c01c2dbaf441f072b07b19caca
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>