aarch64: add HWCAP_ASIMDFHM from linux v4.16

armv8.4 fp mul instructions.
added in commit 3b3b681097fae73b7f5dcdd42db6cfdf32943d4c

arch/aarch64/bits/hwcap.h

@@ -21,3 +21,4 @@
 #define HWCAP_ASIMDDP		(1 << 20)
 #define HWCAP_SHA512		(1 << 21)
 #define HWCAP_SVE		(1 << 22)
+#define HWCAP_ASIMDFHM		(1 << 23)