[WHY]
RV2 and variants are indistinguishable by hw internal rev alone, need to
be distinguishable in order to correctly set max vlevel.  Previous
detection change incorrectly checked for hw internal rev.

[HOW]
Use pci revision to check if RV2 or low power variant Correct a few
overlapping ASICREV range checks
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Reviewed-by: Michael Strauss <Michael.Strauss@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>