efi/ia64: Switch to efi_config_parse_tables()

IA64 calls efi_config_parse_tables() via efi_config_init(), which
does an explicit memremap() of the tables, which is unnecessary
on IA64. So let's call efi_config_parse_tables() directly, passing
the __va() of the config table array.

Tested-by: Tony Luck <tony.luck@intel.com> # arch/ia64
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>