[eMMC]: Make eMMC read and write faster in LK.

 -- Fix the buffer size
 -- Add support to read and write mutiple words at a time
 -- Reduce number of checks for errors.
 -- Increase sdc clock speed for msm8x60

Change-Id: Ied6b6379d9b6d46ed9c4abd8ae1d6ab459ba18a3
4 files changed