mmc: core: Add support to read command queue parameters

eMMC cards with EXT_CSD version >= 7, optionally support command
queuing feature as defined by JEDEC eMMC5.1. Add support for probing
command queue feature for such type of cards.

Change-Id: I9454d0d6997ccbd1778a147354859467f4a9a7d3
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>