aarch64: add HWCAP_ flags from linux v4.17

hwcaps for armv8.4, new in linux commit
7206dc93a58fb76421c4411eefa3c003337bcb2d

arch/aarch64/bits/hwcap.h

@@ -22,3 +22,7 @@
 #define HWCAP_SHA512		(1 << 21)
 #define HWCAP_SVE		(1 << 22)
 #define HWCAP_ASIMDFHM		(1 << 23)
+#define HWCAP_DIT		(1 << 24)
+#define HWCAP_USCAT		(1 << 25)
+#define HWCAP_ILRCPC		(1 << 26)
+#define HWCAP_FLAGM		(1 << 27)