Round of uvm.h cleanup.

The poorly named uvm.h is generally supposed to be for uvm-internal
users only.

- Narrow it to files that actually need it -- mostly files that need
to query whether curlwp is the pagedaemon, which should maybe be
exposed by an external header.

- Use uvm_extern.h where feasible and uvm_*.h for things not exposed
by it. We should split up uvm_extern.h but this will serve for now
to reduce the uvm.h dependencies.

- Use uvm_stat.h and #ifdef UVMHIST uvm.h for files that use
UVMHIST(ubchist), since ubchist is declared in uvm.h but the
reference evaporates if UVMHIST is not defined, so we reduce header
file dependencies.

- Make uvm_device.h and uvm_swap.h independently includable while
here.

ok chs@

UVM locking changes, proposed on tech-kern:

- Change the lock on uvm_object, vm_amap and vm_anon to be a RW lock.
- Break v_interlock and vmobjlock apart. v_interlock remains a mutex.
- Do partial PV list locking in the x86 pmap. Others to follow later.

branches: 1.18.2;
pagedaemon:

- Use marker pages to keep place in the queue when scanning, rather than
relying on assumptions.

- In uvmpdpol_balancequeue(), lock the object once instead of twice.

- When draining pools, the situation is getting desperate, but try to avoid
saturating the system with xcall, lock and interrupt activity by sleeping
for 1 clock tick if being continually awoken and all pools have been
cycled through at least once.

- Pause & resume the freelist cache during pool draining.

PR kern/54209: NetBSD 8 large memory performance extremely low
PR kern/54210: NetBSD-8 processes presumably not exiting
PR kern/54727: writing a large file causes unreasonable system behaviour

branches: 1.17.56;
udpate license clauses on my code to match the new-style BSD licenses.
based on second diff that rmind@ sent me.

no functional change with this commit.

branches: 1.16.2; 1.16.4;
Make "no options VMSWAP" kernels compile again.

branches: 1.15.10; 1.15.28; 1.15.30; 1.15.32;
Merge vmlocking2 to head.

branches: 1.14.4; 1.14.18; 1.14.24; 1.14.26; 1.14.30;
Replace the Mach-derived boolean_t type with the C99 bool type. A
future commit will replace use of TRUE and FALSE with true and false.

branches: 1.13.6;
merge yamt-pdpolicy branch.
- separate page replacement policy from the rest of kernel
- implement an alternative replacement policy

branches: 1.12.8; 1.12.20;
merge ktrace-lwp.

branches: 1.11.2;
fix unreasonably frequent "killed: out of swap" on systems which have
little or no swap.
- even on a severe swap shortage, if we have some amount of file-backed pages,
don't bother to kill processes.
- if all pages in queue will be likely reactivated, just give up
page type balancing rather than spinning unnecessarily.

branches: 1.10.8;
Nuke __P().

branches: 1.9.22;
remove trailing whitespace.

branches: 1.8.6;
Const poison uvm_wait().

branches: 1.7.2; 1.7.4; 1.7.8;
Protect prototypes, certain macros, and inlines from userland.

branches: 1.6.4;
remove now >1 year old pre-release message.

- add defopt's for UVM, UVMHIST and PMAP_NEW.
- remove unnecessary UVMHIST_DECL's.

add/cleanup multiple inclusion protection.

restore rcsids

RCS ID police.

branches: 1.1.1;
Initial revision