8248130: AArch64: pf() uses mtNone instead of mtInternal

[Stefan Karlsson]

Hi all,

Please review this trivial patch to change the NMT flag used by one of 
the debugging functions on AArch64.

https://cr.openjdk.java.net/~stefank/8248130/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8248130

If pf() is used when NMT is turned on we hit this assert:
MallocSite* MallocSiteTable::lookup_or_add(const NativeCallStack& key, 
size_t* bucket_idx,
   size_t* pos_idx, MEMFLAGS flags) {
   assert(flags != mtNone, "Should have a real memory type");

The patch simply changes the used flag to mtInternal.

Thanks,
StefanK