Grab vmobjlocks with RW_DUPOK in vm_obj_wire() to silence WITNESS

Grab vmobjlocks with RW_DUPOK in vm_obj_wire() to silence WITNESS

The drm subsystem implements graphics buffers as uvm objects backed by
anonymous memory, thus drm locks and aobj locks share the same "vmobjlock"
type.

uvm_obj_wire() is only called from sys/dev/pci/drm/, so instead of changing
drm's lock init/alloc routines to mark allow duplicate locks in general,
enter uvm's vmobjlock with RW_DUPOK in this function to allow duplicate
lock types per thread in this specific call path alone.

Fixes the following WITNESS report when booting/starting X (as seen already
in other unrelated bugs@ reports):

wsdisplay0: screen 1-5 added (std, vt100 emulation)
witness: acquiring duplicate lock of same type: "&uobj->vmobjlock"
1st uobjlk
2nd uobjlk
Starting stack trace...
witness_checkorder(fffffd83b625f9b0,9,0) at witness_checkorder+0x8ac
rw_enter(fffffd83b625f9a0,1) at rw_enter+0x68
uvm_obj_wire(fffffd843c39e948,0,40000,ffff800033b70428) at uvm_obj_wire+0x46
shmem_get_pages(ffff800008008500) at shmem_get_pages+0xb8
__i915_gem_object_get_pages(ffff800008008500) at __i915_gem_object_get_pages+0x6d
i915_gem_fault(ffff800008008500,ffff800033b707c0,10009b000,a43d6b1c000,ffff800033b70740,1,35ba896911df1241,ffff8000000aa078,ffff8000000aa178) at i915_gem_fault+0x203
drm_fault(ffff800033b707c0,a43d6b1c000,ffff800033b70740,1,0,0,7eca45006f70ee0,ffff800033b707c0) at drm_fault+0x156
uvm_fault(fffffd843a7cf480,a43d6b1c000,0,2) at uvm_fault+0x179
upageflttrap(ffff800033b70920,a43d6b1c000) at upageflttrap+0x62
usertrap(ffff800033b70920) at usertrap+0x129
recall_trap() at recall_trap+0x8
end of kernel
end trace frame: 0x7f7ffffdc7c0, count: 246
End of stack trace.

Input kettenis
OK mpi