sys/sys/vnode.h: Introduce VOP_PANIC macro for bad VOP's

We later make use of this to reduce some repetition of a
common helper VNOP function that panic's the system on
'bad' VOP's.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/vfs/ufs/ufs_vnops.c: Convert to use VOP_PANIC macro

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/vfs/portal/portal_vnops.c: Convert to use VOP_PANIC macro

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/vfs/deadfs/dead_vnops.c: Convert to use VOP_PANIC macro

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
sys/vfs/fifofs/fifo_vnops.c: Convert to use VOP_PANIC macro

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>