msm: mdss: dp: restrict Vx and Px to within allowable range

Restrict the combinations of voltage swing levels and
pre-emaphasis levels to within the allowable range as per
DP v1.3 specification. Furthermore, set the bits to indicate
the sink when the maximum voltage or pre-emaphasis level
supported has been reached.

CRs-Fixed: 1076516
Change-Id: Ibd5ccc5e24248780df70b5ac7ec7a82511abf688
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>