Make it possible to disable NOP-In PDUs by the iSCSI initiator by setting
kern.cam.ctl.iscsi.ping_timeout to 0.  This fixes interoperability with
some initiators that don't properly support NOP-Ins, namely iPXE/gPXE.

Submitted by:	Chen Wen <pokkys@gmail.com>
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Add more register values to armreg.h and remove CPU_CONTROL_32BP_ENABLE
from asm.h as they were already defined in armreg.h.

Submitted by:	Michal Meloun <meloun at miracle.cz>