openrisc: move board linker script(s) to a common in cpu/

Unifies the openrisc boards linker scripts into a common one.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
diff --git a/arch/openrisc/config.mk b/arch/openrisc/config.mk
index 521e73a..01c0f77 100644
--- a/arch/openrisc/config.mk
+++ b/arch/openrisc/config.mk
@@ -25,3 +25,5 @@
 PLATFORM_CPPFLAGS += -DCONFIG_OPENRISC -D__OR1K__ -ffixed-r10
 
 CONFIG_STANDALONE_LOAD_ADDR ?= 0x40000
+
+LDSCRIPT ?= $(SRCTREE)/$(CPUDIR)/u-boot.lds