avr32: fix linking

This patch fixes following error:

---8<---
avr32-linux-ld: --gc-sections and -r may not be used together
--->8---

Since 8aba9dceebb14144e07d19593111ee3a999c37fc all avr32 boards are broken due
to linking error as seen above.

Signed-off-by: Andreas Bießmann <biessmann@corscience.de>
diff --git a/arch/avr32/config.mk b/arch/avr32/config.mk
index 9488c49..ef14710 100644
--- a/arch/avr32/config.mk
+++ b/arch/avr32/config.mk
@@ -26,4 +26,4 @@
 CONFIG_STANDALONE_LOAD_ADDR ?= 0x00000000
 
 PLATFORM_RELFLAGS	+= -ffixed-r5 -fPIC -mno-init-got -mrelax
-PLATFORM_LDFLAGS	+= --relax
+LDFLAGS_u-boot		= --gc-sections --relax
diff --git a/board/atmel/atngw100/config.mk b/board/atmel/atngw100/config.mk
index ea76d05..c3c7433 100644
--- a/board/atmel/atngw100/config.mk
+++ b/board/atmel/atngw100/config.mk
@@ -1,3 +1,2 @@
 CONFIG_SYS_TEXT_BASE		= 0x00000000
 PLATFORM_RELFLAGS	+= -ffunction-sections -fdata-sections
-PLATFORM_LDFLAGS	+= --gc-sections
diff --git a/board/atmel/atstk1000/config.mk b/board/atmel/atstk1000/config.mk
index 284f7ff..455b0d5 100644
--- a/board/atmel/atstk1000/config.mk
+++ b/board/atmel/atstk1000/config.mk
@@ -1,3 +1,2 @@
 PLATFORM_RELFLAGS	+= -ffunction-sections -fdata-sections
-PLATFORM_LDFLAGS	+= --gc-sections
 CONFIG_SYS_TEXT_BASE		= 0x00000000
diff --git a/board/earthlcd/favr-32-ezkit/config.mk b/board/earthlcd/favr-32-ezkit/config.mk
index 284f7ff..455b0d5 100644
--- a/board/earthlcd/favr-32-ezkit/config.mk
+++ b/board/earthlcd/favr-32-ezkit/config.mk
@@ -1,3 +1,2 @@
 PLATFORM_RELFLAGS	+= -ffunction-sections -fdata-sections
-PLATFORM_LDFLAGS	+= --gc-sections
 CONFIG_SYS_TEXT_BASE		= 0x00000000
diff --git a/board/mimc/mimc200/config.mk b/board/mimc/mimc200/config.mk
index ea76d05..c3c7433 100644
--- a/board/mimc/mimc200/config.mk
+++ b/board/mimc/mimc200/config.mk
@@ -1,3 +1,2 @@
 CONFIG_SYS_TEXT_BASE		= 0x00000000
 PLATFORM_RELFLAGS	+= -ffunction-sections -fdata-sections
-PLATFORM_LDFLAGS	+= --gc-sections
diff --git a/board/miromico/hammerhead/config.mk b/board/miromico/hammerhead/config.mk
index ea76d05..c3c7433 100644
--- a/board/miromico/hammerhead/config.mk
+++ b/board/miromico/hammerhead/config.mk
@@ -1,3 +1,2 @@
 CONFIG_SYS_TEXT_BASE		= 0x00000000
 PLATFORM_RELFLAGS	+= -ffunction-sections -fdata-sections
-PLATFORM_LDFLAGS	+= --gc-sections