x86-64: Move oldrsp from PDA to per-cpu.

tj: * in asm-offsets_64.c, pda.h inclusion shouldn't be removed as pda
      is still referenced in the file
    * s/oldrsp/old_rsp/

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/arch/x86/include/asm/pda.h b/arch/x86/include/asm/pda.h
index 4d28ffb..ae23deb 100644
--- a/arch/x86/include/asm/pda.h
+++ b/arch/x86/include/asm/pda.h
@@ -14,7 +14,7 @@
 	unsigned long unused1;
 	unsigned long unused2;
 	unsigned long unused3;
-	unsigned long oldrsp;		/* 24 user rsp for system call */
+	unsigned long unused4;
 	int irqcount;			/* 32 Irq nesting counter. Starts -1 */
 	unsigned int unused6;		/* 36 was cpunumber */
 #ifdef CONFIG_CC_STACKPROTECTOR