mdss: display: support dcs read with length more than 8 bytes

Add multiple reads per transaction to support dcs read with length
more than 8 bytes.

CRs-Fixed: 525839
Change-Id: I06afa826f941f88c3fe6e2f799c10d12e01708fb
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>