msm: mdss: y offset calc based on format micro tile height

Address offset was using hardcoded micro tile height of 8; Micro
tile height is not fixed and varies from format to format.

Change-Id: Idd033c955997ce56c64861637c60dd8e6f08c61e
Signed-off-by: Terence Hampson <thampson@codeaurora.org>