efi: pstore: move workqueue handling out of efivars

efi: pstore: move workqueue handling out of efivars

The worker thread that gets kicked off to sync the state of the
EFI variable list is only used by the EFI pstore implementation,
and is defined in its source file. So let's move its scheduling
there as well. Since our efivar_init() scan will bail on duplicate
entries, there is no need to disable the workqueue like we did
before, so we can run it unconditionally.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>