drm/amd/display: Parse all extension blocks for VSDB

drm/amd/display: Parse all extension blocks for VSDB

[Why]
VSDB parsing loop only searched within the first extension block.
If the VSDB was located in a subsequent extension block,
it would not be found.

[How]
Calculate the total length of all extension blocks (EDID_LENGTH *
edid->extensions) and use that as the loop boundary, allowing the
parser to search through all available extension blocks.

Reviewed-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>