msm: mdss: avoid padding bytes during DSI commands rx

Currently, for long read response commands, we expect padding
bytes from the panel. However, there might be some panels which
do not support this. Hence, avoid padding bytes during DSI commands
rx and do honest request for reading bytes from the panel. Also due
to this issue, during multiple read requests (expected rlen > 10),
there is possibility that we end up reading same data byte multiple
times and storing it in the rx buffer. Add support to skip the
duplicates by updating the rx data buffer properly.

Change-Id: I2e482924f7275b63d023c947f4a4f27678522e5a
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>