x86: Drop -Wa,--divide

Fix up all the code that is using / to use >> for divisions instead.

Change-Id: I8a6deb0aa090e0df71d90a5509c911b295833cea
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10819
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/mainboard/emulation/qemu-i440fx/cache_as_ram.inc

@@ -36,7 +36,7 @@ cache_as_ram:
        /* Clear the cache memory region. This will also fill up the cache */
 	movl	$CACHE_AS_RAM_BASE, %esi
 	movl	%esi, %edi
-	movl	$(CACHE_AS_RAM_SIZE / 4), %ecx
+	movl	$(CACHE_AS_RAM_SIZE >> 2), %ecx
 	// movl	$0x23322332, %eax
 	xorl	%eax, %eax
 	rep	stosl