wakeup: Switch back to 32bit mode first

On x86_64 we need to leave long mode before we can switch to 16bit
mode. Oh joy! When's my 64bit resume pointer coming?

Why didn't this get caught earlier? Seems the Asrock E350M2 didn't
do Suspend/Resume?

Yes, I know it's Intel syntax. Will be converted to AT&T syntax
as soon as the whole thing actually works.. 8)

Change-Id: Ic51869cf67d842041f8842cd9964d72a024c335f
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/11106
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/arch/x86/wakeup.S

@@ -32,6 +32,34 @@
 
 	.globl __wakeup
 __wakeup:
+#ifdef __x86_64__
+	.intel_syntax noprefix
+	xor     rax,rax
+	mov     ax, ss
+	push    rax
+	mov     rax, rsp
+	add     rax, 8
+	push    rax
+	pushfq
+	push    0x10
+	lea     rax,[rip+3]
+	push    rax
+	iretq
+
+	.code32
+
+	/* disable paging */
+	mov     eax, cr0
+	btc     eax, 31
+	mov     cr0, eax
+
+	/* disable long mode */
+	mov     ecx, 0xC0000080
+	rdmsr
+	btc     eax, 8
+	wrmsr
+	.att_syntax prefix
+#endif
 	/* First prepare the jmp to the resume vector */
 	mov	0x4(%esp), %eax	/* vector */
 	/* last 4 bits of linear addr are taken as offset */