[IA64] pvops: preparation: introduce ia64_get_psr_i() to make kernel paravirtualization friendly.

__local_irq_save() and local_save_flags() are used to mask interruptions.
They read all psr bits that requres whole bit emulation.
On the other hand, reading only psr.i, the single bit, can be virtualized
cheaply.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>