ppc4xx: Add custom linker script to board/*/config.mk

These boards have special linker scripts right now. We can't use the
common 4xx linker script here. So overrride the linker script (LDSCRIPT)
in board/*/config.mk and choose the board specific version.

Signed-off-by: Stefan Roese <sr@denx.de>

board/amirix/ap1000/config.mk

@@ -25,3 +25,6 @@
 # like it's not in RAM.  This is a bit of voodoo to allow it to be
 # run from RAM instead of Flash.
 TEXT_BASE = 0x08000000
+
+# Use board specific linker script
+LDSCRIPT := $(SRCTREE)/board/amirix/ap1000/u-boot.lds

board/esd/dasa_sim/config.mk

@@ -21,3 +21,6 @@
 # MA 02111-1307 USA
 #
 TEXT_BASE = 0xFFFC0000
+
+# Use board specific linker script
+LDSCRIPT := $(SRCTREE)/board/esd/dasa_sim/u-boot.lds

board/ml2/config.mk

@@ -27,3 +27,6 @@
 
 #TEXT_BASE = 0xFFFE0000
 TEXT_BASE = 0x18000000
+
+# Use board specific linker script
+LDSCRIPT := $(SRCTREE)/board/ml2/u-boot.lds

board/xilinx/ml300/config.mk

@@ -27,3 +27,6 @@
 
 #TEXT_BASE = 0xFFFE0000
 TEXT_BASE = 0x04000000
+
+# Use board specific linker script
+LDSCRIPT := $(SRCTREE)/board/xilinx/ml300/u-boot.lds