ANDROID: drm: Add support for DP 1.4 Compliance edid corruption test

Unlike DP 1.2 edid corruption test, DP 1.4 requires to calculate
real CRC value of the last edid data block, and write it back.
Current edid CRC calculates routine adds the last CRC byte,
and check if non-zero.

This behavior is not accurate; actually, we need to return
the actual CRC value when corruption is detected.
This commit changes this issue by returning the calculated CRC,
and initiate the required sequence.

Change since v5
- Obtain real CRC value before dumping bad edid

Change since v4
- Fix for CI.CHECKPATCH

Change since v3
- Fix a minor typo.

Change since v2
- Rewrite checksum computation routine to avoid duplicated code.
- Rename to avoid confusion.

Change since v1
- Have separate routine for returning real CRC.

Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
[adelva: resolved conflict with android-5.4's drm_dp_helper.h]
Bug: 139653858
Link: https://patchwork.freedesktop.org/patch/351454/


Change-Id: Ib93f7cc21d77e29d6846a44de4368d96c50f5682
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Alistair Delva <adelva@google.com>