Add support for a saving build objects in a separate directory.
Modifications are based on the linux kernel approach and
support two use cases:

  1) Add O= to the make command line
  'make O=/tmp/build all'

  2) Set environement variable BUILD_DIR to point to the desired location
  'export BUILD_DIR=/tmp/build'
  'make'

The second approach can also be used with a MAKEALL script
'export BUILD_DIR=/tmp/build'
'./MAKEALL'

Command line 'O=' setting overrides BUILD_DIR environent variable.

When none of the above methods is used the local build is performed and
the object files are placed in the source directory.
diff --git a/board/integratorap/config.mk b/board/integratorap/config.mk
index 25b79b3..e4c5c3b 100644
--- a/board/integratorap/config.mk
+++ b/board/integratorap/config.mk
@@ -3,3 +3,9 @@
 #
 
 TEXT_BASE = 0x01000000
+
+ifneq ($(OBJTREE),$(SRCTREE))
+# We are building u-boot in a separate directory, use generated
+# .lds script from OBJTREE directory.
+LDSCRIPT := $(OBJTREE)/board/$(BOARDDIR)/u-boot.lds
+endif