nb/intel/sandybridge: Fix PEG disablement

Fix regression introduced by:
3660c0fc65
"northbridge/intel/sandybridge: Enable PEG clock-gating on demand"

Issue observed:
GNU/Linux kernel crashes in earlyinit on systems without PEG devices.
The crash occurs on every boot in different functions.
There's no problem on systems with PEG enabled.

Test system:
 * Lenovo T530
 * Intel Core i5-3320M CPU
 * Fedora GNU/Linux 4.1
 * PEG disabled in devicetree

Problem description:
Tests shows that modifing PEG chicken bit or device enable bits
after setting BIOS_RESET_CPL causes random crashes in GNU/Linux.

Problem solution:
Disable PEG devices before setting BIOS_RESET_CPL.

Final testing results:
No more random kernel crashes.

Change-Id: I4a967c2d00d7d1e4426cf5abdd5f616c21557da7
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: http://review.coreboot.org/12112
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>
(cherry picked from commit aad34cda4b)
Reviewed-on: https://review.coreboot.org/12456
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/northbridge/intel/sandybridge/northbridge.c

@@ -431,6 +431,11 @@ static void northbridge_init(struct device *dev)
 	}
 	MCHBAR32(0x5f10) = bridge_type;
 
+	/* Turn off unused devices. Has to be done before
+	 * setting BIOS_RESET_CPL.
+	 */
+	disable_peg();
+
 	/*
 	 * Set bit 0 of BIOS_RESET_CPL to indicate to the CPU
 	 * that BIOS has initialized memory and power management
@@ -456,9 +461,6 @@ static void northbridge_init(struct device *dev)
 
 	/* Set here before graphics PM init */
 	MCHBAR32(0x5500) = 0x00100001;
-
-	/* Turn off unused devices */
-	disable_peg();
 }
 
 static void northbridge_enable(device_t dev)