arch/x86: Replace plain strings with constants

We've got constants, so let's use them instead of hard-coded values.
Signed-off-by: NDaniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>

arch/x86/kernel/setup.c

@@ -924,10 +924,10 @@ void __init setup_arch(char **cmdline_p)
 #endif
 #ifdef CONFIG_EFI
 	if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,
-		     "EL32", 4)) {
+		     EFI32_LOADER_SIGNATURE, 4)) {
 		set_bit(EFI_BOOT, &efi.flags);
 	} else if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,
-		     "EL64", 4)) {
+		     EFI64_LOADER_SIGNATURE, 4)) {
 		set_bit(EFI_BOOT, &efi.flags);
 		set_bit(EFI_64BIT, &efi.flags);
 	}