nyan: Use asm volatile instead of plain asm so it doesn't get optimized out.

If an asm blob isn't marked as volatile, gcc is free to throw it out if it
doesn't think it produces any values that are actually used. To prevent that
from happening, add volatile to some asm blobs in the nyan romstage code.

BUG=None
TEST=Booted on nyan rev1.
BRANCH=None

Original-Change-Id: I819e068e738e94ea749fcb72bba2eee080e1dfb1
Original-Signed-off-by: Gabe Black <gabeblack@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/185610
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Original-Commit-Queue: Gabe Black <gabeblack@chromium.org>
Original-Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 76c09581d6ca4dc6c2f9048f599822939f439d11)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I0b32197abf0ddc5f454f9c2415a65d98c60ca48b
Reviewed-on: http://review.coreboot.org/7396
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)

src/mainboard/google/nyan/romstage.c

@@ -136,6 +136,7 @@ static void __attribute__((noinline)) romstage(void)
 /* Stub to force arm_init_caches to the top, before any stack/memory accesses */
 void main(void)
 {
-	asm ("bl arm_init_caches" ::: "r0","r1","r2","r3","r4","r5","ip");
+	asm volatile ("bl arm_init_caches"
+		      ::: "r0","r1","r2","r3","r4","r5","ip");
 	romstage();
 }

src/mainboard/google/nyan_big/romstage.c

@@ -136,6 +136,7 @@ static void __attribute__((noinline)) romstage(void)
 /* Stub to force arm_init_caches to the top, before any stack/memory accesses */
 void main(void)
 {
-	asm ("bl arm_init_caches" ::: "r0","r1","r2","r3","r4","r5","ip");
+	asm volatile ("bl arm_init_caches"
+		      ::: "r0","r1","r2","r3","r4","r5","ip");
 	romstage();
 }