[IA64] Don't set psr.ic and psr.i simultaneously

It's not a good idea to use "ssm psr.ic | psr.i" to simultaneously
enable interrupts and interrupt state collection, the two bits can
take effect asynchronously, so it is possible for an interrupt to
be serviced while psr.ic is still zero.

Signed-off-by: Tony Luck <tony.luck@intel.com>