fsp_baytrail: Allow selection of USB controller by get_option

It was requested to be able to update XHCI vs EHCI via get_option,
so I've added it here for minnow max.  This could get moved to the
chipset_fsp_util.c file later, but I'm adding it here for now.

More checking needs to be added to this:
- Are both controllers enabled in devicetree?  If not, we don't want
to allow the switch.

Change-Id: I4d8d2229cb9fa0cd9068701454b28ffac6d8e767
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/7633
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
diff --git a/src/mainboard/intel/minnowmax/cmos.layout b/src/mainboard/intel/minnowmax/cmos.layout
index a668188..c7dc88d 100644
--- a/src/mainboard/intel/minnowmax/cmos.layout
+++ b/src/mainboard/intel/minnowmax/cmos.layout
@@ -85,7 +85,8 @@
 # coreboot config options: southbridge
 408          1       e       1        nmi
 409          2       e       7        power_on_after_fail
-#411          5       r       0        unused
+411          2       e       8        use_xhci_over_ehci
+#413          3       r       0        unused
 
 # MRC Scrambler Seed values
 896         32        r       0        mrc_scrambler_seed
@@ -133,6 +134,9 @@
 7     0     Disable
 7     1     Enable
 7     2     Keep
+8     0     EHCI
+8     1     XHCI
+8     2     Default
 # -----------------------------------------------------------------
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