sunxi: Add a GMAC Transmit Clock Delay Chain Kconfig option

And use this to set the GMAC Transmit Clock Delay Chain value on Banana
boards, rather then keying of CONFIG_TARGET_FOO.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig
index f48b8c0..15e3d46 100644
--- a/board/sunxi/Kconfig
+++ b/board/sunxi/Kconfig
@@ -380,4 +380,10 @@
 	Say Y here to add support for using a USB keyboard (typically used
 	in combination with a graphical console).
 
+config GMAC_TX_DELAY
+	int "GMAC Transmit Clock Delay Chain"
+	default 0
+	---help---
+	Set the GMAC Transmit Clock Delay Chain value.
+
 endif