drm/radeon/dpm: add a helper to encode pcie lane setting

convert from number of lanes to register setting.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/r600_dpm.c

@@ -1246,3 +1246,13 @@ u16 r600_get_pcie_lane_support(struct radeon_device *rdev,
 		return 16;
 	}
 }
+
+u8 r600_encode_pci_lane_width(u32 lanes)
+{
+	u8 encoded_lanes[] = { 0, 1, 2, 0, 3, 0, 0, 0, 4, 0, 0, 0, 5, 0, 0, 0, 6 };
+
+	if (lanes > 16)
+		return 0;
+
+	return encoded_lanes[lanes];
+}

drivers/gpu/drm/radeon/r600_dpm.h

@@ -227,5 +227,6 @@ enum radeon_pcie_gen r600_get_pcie_gen_support(struct radeon_device *rdev,
 u16 r600_get_pcie_lane_support(struct radeon_device *rdev,
 			       u16 asic_lanes,
 			       u16 default_lanes);
+u8 r600_encode_pci_lane_width(u32 lanes);
 
 #endif