drm/edid: add checksum to connector

Add checksum of an associated EDID block to the connector.
The calculated value of checksum may be useful in cases of
a corrupted EDID where the checksum value in 128th byte is
not correct and a correct value is needed by the client.
For example, DP 1.4a CTS 4.2.2.6 test needs the correct
EDID checksum to be updated to the TE (Test Equipment).

Change-Id: If1a2931be9103f45b5044d637362f34ce60a7ba0
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>