efi: initialize efi.runtime_version to make query_variable_info/update_capsule workable

A value of efi.runtime_version is checked before calling
update_capsule()/query_variable_info() as follows.
But it isn't initialized anywhere.

<snip>
static efi_status_t virt_efi_query_variable_info(u32 attr,
                                                 u64 *storage_space,
                                                 u64 *remaining_space,
                                                 u64 *max_variable_size)
{
        if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
                return EFI_UNSUPPORTED;
<snip>

This patch initializes a value of efi.runtime_version at boot time.
Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Acked-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

arch/x86/platform/efi/efi.c

@@ -890,6 +890,7 @@ void __init efi_enter_virtual_mode(void)
 	 *
 	 * Call EFI services through wrapper functions.
 	 */
+	efi.runtime_version = efi_systab.fw_revision;
 	efi.get_time = virt_efi_get_time;
 	efi.set_time = virt_efi_set_time;
 	efi.get_wakeup_time = virt_efi_get_wakeup_time;