Allow arch directory to contain .lds without requiring Makefile

The Makefile for a CPU is in arch/($ARCH)/cpu/$(CPU). We want to support
having an .lds file in arch/$(ARCH)/cpu without requiring an additional
Makefile there. This change makes it clear that we expect a Makefile in
the same directory as the link script except in this case.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/spl/Makefile b/spl/Makefile
index 3262e22..680f6dd 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -81,6 +81,9 @@
 	LDSCRIPT := $(TOPDIR)/$(CPUDIR)/u-boot-spl.lds
 endif
 ifeq ($(wildcard $(LDSCRIPT)),)
+	LDSCRIPT := $(TOPDIR)/arch/$(ARCH)/cpu/u-boot.lds
+endif
+ifeq ($(wildcard $(LDSCRIPT)),)
 $(error could not find linker script)
 endif