x86/AMD: work around erratum 793 for 32-bit

The original change went into a 64-bit only code section, thus leaving
the issue unfixed on 32-bit. Re-order code to address this.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>

--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -522,6 +522,18 @@ static void __devinit init_amd(struct cp
 		       "*** Pass \"allow_unsafe\" if you're trusting"
 		       " all your (PV) guest kernels. ***\n");
 
+	/* AMD CPUs do not support SYSENTER outside of legacy mode. */
+	clear_bit(X86_FEATURE_SEP, c->x86_capability);
+
+	if (c->x86 == 0x10) {
+		/* do this for boot cpu */
+		if (c == &boot_cpu_data)
+			check_enable_amd_mmconf_dmi();
+
+		fam10h_check_enable_mmcfg();
+	}
+#endif
+
 	if (c->x86 == 0x16 && c->x86_model <= 0xf) {
 		if (c == &boot_cpu_data) {
 			l = pci_conf_read32(0, 0, 0x18, 0x3, 0x58);
@@ -555,18 +567,6 @@ static void __devinit init_amd(struct cp
 		}
 	}
 
-	/* AMD CPUs do not support SYSENTER outside of legacy mode. */
-	clear_bit(X86_FEATURE_SEP, c->x86_capability);
-
-	if (c->x86 == 0x10) {
-		/* do this for boot cpu */
-		if (c == &boot_cpu_data)
-			check_enable_amd_mmconf_dmi();
-
-		fam10h_check_enable_mmcfg();
-	}
-#endif
-
 	if (c->x86 == 0x10) {
 		/*
 		 * On family 10h BIOS may not have properly enabled WC+