Make STANDALONE_LOAD_ADDR configurable per board

Rename STANDALONE_LOAD_ADDR into CONFIG_STANDALONE_LOAD_ADDR
and allow that the architecture-specific default value gets
overwritten by defining the value in the board header file.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>
Cc: Daniel Hellstrom <daniel@gaisler.com>
Cc: Tsi Chung Liew <tsi-chung.liew@freescale.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/arch/powerpc/config.mk b/arch/powerpc/config.mk
index 8d72fbd..3afc439 100644
--- a/arch/powerpc/config.mk
+++ b/arch/powerpc/config.mk
@@ -23,7 +23,7 @@
 
 CROSS_COMPILE ?= ppc_8xx-
 
-STANDALONE_LOAD_ADDR = 0x40000
+CONFIG_STANDALONE_LOAD_ADDR ?= 0x40000
 LDFLAGS_FINAL += --gc-sections
 PLATFORM_RELFLAGS += -fpic -mrelocatable -ffunction-sections -fdata-sections
 PLATFORM_RELFLAGS += $(call cc-option,-msingle-pic-base,)