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/Bananapi_defconfig b/configs/Bananapi_defconfig
index d94e08e..4cff573 100644
--- a/configs/Bananapi_defconfig
+++ b/configs/Bananapi_defconfig
@@ -1,6 +1,7 @@
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="AXP209_POWER,SUNXI_GMAC,RGMII,MACPWR=SUNXI_GPH(23),AHCI,USB_EHCI"
 CONFIG_FDTFILE="sun7i-a20-bananapi.dtb"
+CONFIG_GMAC_TX_DELAY=3
 +S:CONFIG_ARM=y
 +S:CONFIG_ARCH_SUNXI=y
 +S:CONFIG_MACH_SUN7I=y