drm/msm/dp: add support for electrical compliance tests

Add support for electrical compliance tests by reading the
test request parameters and configuring the DP PHY to generate
the requested test pattern.

CRs-Fixed: 2094794
Change-Id: I43fb6e5303ff45c5738cd3d98fdc29aa4ddd3450
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>