aarch64: add HWCAP_DCPOP from linux v4.14

indicates ARMv8.2-DCPoP persistent memory support extension.
new in linux commit 7aac405ebb3224037efd56b73d82d181111cdac3

arch/aarch64/bits/hwcap.h

@@ -14,3 +14,4 @@
 #define HWCAP_JSCVT		(1 << 13)
 #define HWCAP_FCMA		(1 << 14)
 #define HWCAP_LRCPC		(1 << 15)
+#define HWCAP_DCPOP		(1 << 16)