disp: msm: dp: enhance dpcd debugfs to parse extended capability information

Add support to pass extended capability information to the DPCD
debugfs node. This will help to validate features like VSC support
using debugfs node.

Usage will be the same as before and the change will automatically
detect the presence of extended capability field and expect
additional bytes of information.

Change-Id: If541fd8837aac4794c3db0fa3badeab4143ff9c3
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>