sb/intel/bd82x6x/early_usb.c: Align native current map with MRC

Replace 3 unused values in the map with those found during a Ghidra
examination of MRC binary, and on hardwares running vendor firmware
(asus/p8z77-m and HP Z210 CMT Workstation).

The outgoing values were introduced in commit 216ad2170ca8
("sb/intel/bd82x6x: Add new USB currents") in anticipation for
Gigabyte GA-Z77-DS3H mainboard, but effort to land it was eventually
abandoned. Since commit xxxxxxxxxxxx, such values can be placed
directly in the port config, so there should be no hurdle should that
effort be resurrected.

Add a few #defines in pch.h to place some inline documentation
on MRC values, but more will be documented in the future when this
mapping is introduced MRC-side.

Finally, update autoport to match.

Change-Id: I195c7f627994e48f7a6e6698589504dc96248cff
Signed-off-by: Keith Hui <buurin@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82754
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <patrick.rudolph@9elements.com>
diff --git a/util/autoport/bd82x6x.go b/util/autoport/bd82x6x.go
index 76411e7..e2dc827 100644
--- a/util/autoport/bd82x6x.go
+++ b/util/autoport/bd82x6x.go
@@ -311,8 +311,8 @@
 		0x2000094a: 4,
 		0x2000035f: 5,
 		0x20000f53: 6,
-		0x20000357: 7,
-		0x20000353: 8,
+		0x20000f5b: 7,
+		0x20000553: 9,
 	}
 
 	for port := uint(0); port < 14; port++ {