_info()->flags, prefetch
	    kernel register-backing store) and switch
	    to kernel register-stack.
 - Phase 3: Call ia64_syscall_setup() and invoke
	    syscall-handler.

Good for 26-30 cycles of improvement on break-based syscall-path.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
k