disp: msm: dp: add support for test pattern #4

DP specification mandate test pattern #4 for CTS 1.4a. Add
support for the same in link training #2 as per specification.

CRs-Fixed: 2490128
Change-Id: I2f72fec340b56270e7fd1c2940adafe1068bab43
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>