MFC r263475:
Fix two issues with /dev/mem access on amd64, both causing kernel page
faults.

First, for accesses to direct map region should check for the limit by
which direct map is instantiated.

Second, for accesses to the kernel map, use a new thread private flag
TDP_DEVMEMIO, which instructs vm_fault() to return error when fault
happens on the MAP_ENTRY_NOFAULT entry, instead of panicing.

MFC r263498:
Add change forgotten in r263475.  Make dmaplimit accessible outside
amd64/pmap.c.
MFC r262912

cddl/contrib/opensolaris/lib/libuutil/common/uu_avl.c
	Fix a memory leak in uu_avl_pool_create: pthread_mutex_init without
	a corresponding pthread_mutex_destroy.  It shows up, among other
	places, when doing "zfs list