ARM: zImage: Fix bad SP address after relocating kernel

Otherwise cache_clean_flush can overwrite some of the relocated
area depending on where the kernel image gets loaded. This fixes
booting on n900 after commit 6d7d0ae5
(ARM: 6750/1: improvements to compressed/head.S).

Thanks to Aaro Koskinen <aaro.koskinen@nokia.com> for debugging
the address of the relocated area that gets corrupted, and to
Nicolas Pitre <nicolas.pitre@linaro.org> for the other uncompress
related fixes.
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

arch/arm/boot/compressed/head.S

@@ -253,6 +253,11 @@ restart:	adr	r0, LC0
 		/* Preserve offset to relocated code. */
 		sub	r6, r9, r6
 
+#ifndef CONFIG_ZBOOT_ROM
+		/* cache_clean_flush may use the stack, so relocate it */
+		add	sp, sp, r6
+#endif
+
 		bl	cache_clean_flush
 
 		adr	r0, BSYM(restart)