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/configs/Bananapro_defconfig b/configs/Bananapro_defconfig
index 02e4f3e..0512019 100644
--- a/configs/Bananapro_defconfig
+++ b/configs/Bananapro_defconfig
@@ -3,6 +3,7 @@
 CONFIG_FDTFILE="sun7i-a20-bananapro.dtb"
 CONFIG_USB1_VBUS_PIN="PH0"
 CONFIG_USB2_VBUS_PIN="PH1"
+CONFIG_GMAC_TX_DELAY=3
 +S:CONFIG_ARM=y
 +S:CONFIG_ARCH_SUNXI=y
 +S:CONFIG_MACH_SUN7I=y