BugLink: http://bugs.launchpad.net/bugs/1546572

Use atombios to calculate the values.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d39d5c2c)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>