mmc: add a library function to send tuning command

mmc: add a library function to send tuning command

HS200/SDR104 requires tuning command to be sent to the card.
Add a simple function to send tuning command and to read and
compare the received data with the tuning block pattern.
This function can be used by platform driver to perform DLL
tuning.
This patch is similar to
commit 996903de92f0 ("mmc: core: add core-level function for
sending tuning commands") added in linux kernel.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>