efi: Make efi_rts_work accessible to efi page fault handler

After the kernel has booted, if any accesses by firmware causes a page
fault, the efi page fault handler would freeze efi_rts_wq and schedules
a new process. To do this, the efi page fault handler needs
efi_rts_work. Hence, make it accessible.

There will be no race conditions in accessing this structure, because
all the calls to efi runtime services are already serialized.

Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
Suggested-by: Matt Fleming <matt@codeblueprint.co.uk>
Based-on-code-from: Ricardo Neri <ricardo.neri@intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>