efi: ia64: move IA64-only declarations to new asm/efi.h header

Move some EFI related declarations that are only referenced on IA64 to
a new asm/efi.h arch header.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>