drm/amdgpu:Fix EEPROM checksum calculation.

Fix checksum calculation after manually resetting the table.
Unify reset and empty EEPROM init flow.
Protect the table reset with lock.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>