arm: mvebu: a38x: Configurable USB2 high-speed impedance threshold

Hardware testing of a board using the Armada 385 has shown that an
impedance threshold setting of 0x7 performs better in an eye-diagram
test than with Marvell's recommended value 0x6.

As other boards may still perform better with Marvell's reccomended value,
a configuration option is added with a default value of 0x6.

Signed-off-by: Joshua Scott <joshua.scott@alliedtelesis.co.nz>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/arm/mach-mvebu/Kconfig b/arch/arm/mach-mvebu/Kconfig
index 0d8e092..72aee8b 100644
--- a/arch/arm/mach-mvebu/Kconfig
+++ b/arch/arm/mach-mvebu/Kconfig
@@ -30,6 +30,12 @@
 	select ARMADA_32BIT
 	select HAVE_MVEBU_EFUSE
 
+config ARMADA_38X_HS_IMPEDANCE_THRESH
+	hex  "Armada 38x USB 2.0 High-Speed Impedance Threshold (0x0 - 0x7)"
+	depends on ARMADA_38X
+	default 0x6
+	range 0x0 0x7
+
 config ARMADA_XP
 	bool
 	select ARMADA_32BIT