64-bit vkernel

[Jordan Gordeev <jgordeev@xxxxxx>]

The code for the 64-bit vkernel is now available from my leaf repo 
(git://leaf.dragonflybsd.org/~smtms/dragonfly.git), branch 'vkernel2'.
It works pretty ok.
I'm leaving it to you guys to do the integration work.
The pmap code should be reviewed by Matt.

As this is the end of my involvement with DragonFly, I'm listing a few 
things from my to do list here, in the hope that they'll be taken care of:
 - see how well OFF_TO_IDX() works for pc64 kernel addresses
 - when the pc64 kernel handles a trap or a syscall, it creates a 
'struct trapframe' on the stack. Check to see if the stack is properly 
aligned, as required by the AMD64 ABI, when we call trap() or syscall2().
 - make sure that addresses not in canonical address form are handled 
correctly for user processes under the 64-bit vkernel and for the 64-bit 
vkernel itself.
 - the way 'nkpt' is used in pmap_growkernel() in the 64-bit vkernel is 
wrong. Fix it.

Farewell!