Don't use a stack based DPC structure in the System per-CPU code
Don't use a stack based DPC structure in the System per-CPU code

Whilst this is believed to be safe, there is no documentation to say that
Windows does not make use of the DPC structure after the DPC routine has
completed. Instead, make the DPC structure part of the per-CPU structure.

Also fix an ASSERT on the per-CPU array pointer not being NULLed.

Signed-off-by: Paul Durrant <dba6cd059c0054f8a3c62ba902cd9d7238853ee4@citrix.com>

omeg/xenbus,QubesOS/qubes-vmm-xen-win-pvdrivers-xenbus,rneilturner/xenbus,QubesOS/qubes-vmm-xen-win-pvdrivers-xenbus,omeg/xenbus,rneilturner/xenbus,omeg/xenbus,MarkKMueller/xenbus,QubesOS/qubes-vmm-xen-win-pvdrivers-xenbus,MarkKMueller/xenbus,MarkKMueller/xenbus,rneilturner/xenbus