davinci: mmc: add a function to control reset state of the controller

Add a helper function which will aid in changing the reset
status of the controller.

Signed-off-by: Chaithrika U S <chaithrika@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Vipin Bhandari <vipin.bhandari@ti.com>
Cc: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>