[IA64] kexec: Use a separate RID for EFI

[IA64] kexec: Use a separate RID for EFI

This activates the use of the EFI RID.

The basic idea is to switch to this RID, which is in the range reserved
for the hypervisor, before making EFI, PAL or SAL calls. The page fault
handler where the identity mapping checks for this RID, if present it
does the identity mapping, else it just follows the normal mapping
rules. In this way, VMX domains should not be able to access this
memory, and they should be able to use the virtual addresses that are
used by EFI for their own purposes.

Subsequent patches move EFI memory such that faults to it will
be protected by the EFI RID.

Cc: Tristan Gingold <tgingold@free.fr>
Cc: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Alex Williamson <alex.williamson@hp.com>
Cc: Aron Griffis <aron@hp.com>
Signed-off-by: Simon Horman <horms@verge.net.au>