sunxi: Remove CONFIG_TARGET_FOO for sun5i and sun7i boards

CONFIG_TARGET_FOO was only used in board/sunxi/Makefile to select the
dram config for sun5i and sun7i boards and in board/sunxi/gmac.c for some
special handling of the bananapi/bananapro (both sun7i), all sun5i and sun7i
boards have been moved over to using a single dram_sun5i_autoconfig file,
and the tx clk delay handling for the Banana boards now has its own Kconfig.

IOW nothing is using CONFIG_TARGET_FOO anymore, so remove it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>

configs/MSI_Primo73_defconfig

@@ -1,3 +1,11 @@
+# The MSI Primo73 is an A20 based tablet, with 1G RAM, 16G NAND,
+# 1024x600 TN LCD display, mono speaker, 0.3 MP front camera, 2.0 MP
+# rear camera, 3000 mAh battery, gt911 touchscreen, mma8452 accelerometer
+# and rtl8188etv usb wifi. Has "power", "volume+" and "volume-" buttons
+# (both volume buttons are also connected to the UBOOT_SEL pin). The
+# external connectors are represented by MicroSD slot, MiniHDMI, MicroUSB
+# OTG and 3.5mm headphone jack. More details are available at
+#    http://linux-sunxi.org/MSI_Primo73
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="AXP209_POWER"
 CONFIG_FDTFILE="sun7i-a20-primo73.dtb"
@@ -10,7 +18,6 @@ CONFIG_USB_KEYBOARD=n
 +S:CONFIG_ARM=y
 +S:CONFIG_ARCH_SUNXI=y
 +S:CONFIG_MACH_SUN7I=y
-+S:CONFIG_TARGET_MSI_PRIMO73=y
 +S:CONFIG_DRAM_CLK=384
 +S:CONFIG_DRAM_ZQ=127
 +S:CONFIG_DRAM_EMR1=4