[IA64] fix fpswa mapping which was broken by EFI mapping.

[IA64] fix fpswa mapping which was broken by EFI mapping.

This patch fixes the following panic reported by Kusamura when xen
VMM tries to use fpswa.
With the EFI mapping patch, all the firmware call is done in
the dedicated address space.
fpswa is EFI driver so that the address space must be switched
before/after calling fpswa.

> (XEN) $$$$$ PANIC in domain 2 (k6=0xf0000004f25e8000): *** xen_handle_domain_access: exception table lookup failed, iip=0xf40000000408cc30,
> addr=0xe0000004ffe62050, spinning...
> (XEN) d 0xf000000004138080 domid 2
> (XEN) vcpu 0xf0000004f25e8000 vcpu 0
> (XEN)
> (XEN) CPU 5
> (XEN) psr : 0000121008226038 ifs : 8000000000000716 ip  : [<f40000000408cc31>]
> (XEN) ip is at handle_fpu_swa+0x3c1/0x510
...

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>