spl: Add an SPL_HAVE_INIT_STACK option

At present there is a hex value SPL_STACK which both determines whether
SPL has its own initial stack and the hex value of that stack.

Split off the former into SPL_HAVE_INIT_STACK with SPL_STACK depending
on that and only providing the latter.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Resync defconfig files]
diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index aca5b86..0248606 100644
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -102,7 +102,7 @@
 
 #if defined(CONFIG_TPL_BUILD) && defined(CONFIG_TPL_HAVE_INIT_STACK)
 	ldr	r0, =(CONFIG_TPL_STACK)
-#elif defined(CONFIG_XPL_BUILD) && defined(CONFIG_SPL_STACK)
+#elif defined(CONFIG_XPL_BUILD) && defined(CONFIG_SPL_HAVE_INIT_STACK)
 	ldr	r0, =(CONFIG_SPL_STACK)
 #else
 	ldr	r0, =(SYS_INIT_SP_ADDR)