omap4-hsmmc : Adding ADMA support

Adds ADMA support for HSMMC controllers 1 & 2 on OMAP4
Ensure dma-sg list coming from block layer is unmapped after
every transfer completion.

Change-Id: I1b898f771a3119804920c5cd17ec9c4456c60916
Signed-off-by: Viswanath Puttagunta <vishp@ti.com>
Signed-off-by: Kishore Kadiyala <kishore.kadiyala@ti.com>
Signed-off-by: David Taylor <x0158378@ti.com>