Reduce the number of attempts to detect proper kld format for the amd64

loader.

sys/boot/i386/loader/Makefile

@@ -125,6 +125,7 @@ LDADD=	${LIBFICL} ${LIBFIREWIRE} ${LIBZFSBOOT} ${LIBI386} ${LIBSTAND}
 .if ${MACHINE_CPUARCH} == "amd64"
 beforedepend ${OBJS}: machine
 CLEANFILES+=	machine
+CFLAGS+=	-DLOADER_PREFER_AMD64
 machine:
 	ln -sf ${.CURDIR}/../../../i386/include machine
 .endif

sys/boot/i386/loader/conf.c

@@ -109,10 +109,16 @@ extern struct file_format	amd64_elf;
 extern struct file_format	amd64_elf_obj;
 
 struct file_format *file_formats[] = {
-    &i386_elf,
-    &i386_elf_obj,
+#ifdef LOADER_PREFER_AMD64
     &amd64_elf,
     &amd64_elf_obj,
+#endif
+    &i386_elf,
+    &i386_elf_obj,
+#ifndef LOADER_PREFER_AMD64
+    &amd64_elf,
+    &amd64_elf_obj,
+#endif
     NULL
 };