x86, microcode, AMD: Add microcode revision to /proc/cpuinfo

Enable microcode revision output for AMD after 506ed6b53e00 ("x86,
intel: Output microcode revision in /proc/cpuinfo") did it for Intel.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index b13ed39..d898fab 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -412,6 +412,8 @@
 
 static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
 {
+	u32 dummy;
+
 	early_init_amd_mc(c);
 
 	/*
@@ -442,6 +444,8 @@
 	}
 #endif
 
+	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
+
 	/* We need to do the following only once */
 	if (c != &boot_cpu_data)
 		return;