drm/amd/pm: Update pci link speed for smu v13.0.6

Update pcie link speed registers for smu v13.0.6 &
populate gpu metric table with pcie link speed rather than
gen for smu v13_0_0, smu v13_0_6 & smu v13_0_7

v2:
Update ESM register address
Used macro to convert pcie gen to speed

v3:
Chaged macro to inline function for pcie gen to speed

Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>