x86, cpu: Add SMEP CPU feature in CR4

Add support for newly documented SMEP (Supervisor Mode Execution Protection)
CPU feature in CR4.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
LKML-Reference: <1305683069-25394-3-git-send-email-fenghua.yu@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/processor-flags.h

@@ -60,6 +60,7 @@
 #define X86_CR4_OSXMMEXCPT 0x00000400 /* enable unmasked SSE exceptions */
 #define X86_CR4_VMXE	0x00002000 /* enable VMX virtualization */
 #define X86_CR4_OSXSAVE 0x00040000 /* enable xsave and xrestore */
+#define X86_CR4_SMEP	0x00100000 /* enable SMEP support */
 
 /*
  * x86-64 Task Priority Register, CR8