Eliminate the counting of vm_page_pa_tryrelock calls. We really don't

Eliminate the counting of vm_page_pa_tryrelock calls.  We really don't
need it anymore.  Moreover, its implementation had a type mismatch, a
long is not necessarily an uint64_t.  (This mismatch was hidden by
casting.)  Move the remaining two counters up a level in the sysctl
hierarchy.  There is no reason for them to be under the vm.pmap node.

Reviewed by:	kib