efi/arm64: Store Runtime Services revision

"efi" global data structure contains "runtime_version" field which must
be assigned in order to use it later in Runtime Services virtual calls
(virt_efi_* functions).

Before this patch "runtime_version" was unassigned (0), so each
Runtime Service virtual call that checks revision would fail.

Signed-off-by: Semen Protsenko <semen.protsenko@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>