[Why]
The original coasting vtotal is 2 bytes, and it need to be amended to 4
bytes because low hz case.

[How]
Amend coasting vtotal from 2 bytes to 4 bytes.
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: ChunTao Tso <ChunTao.Tso@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>