efi: vars: Move efivar caching layer into efivarfs

Move the fiddly bits of the efivar layer into its only remaining user,
efivarfs, and confine its use to that particular module. All other uses
of the EFI variable store have no need for this additional layer of
complexity, given that they either only read variables, or read and
write variables into a separate GUIDed namespace, and cannot be used to
manipulate EFI variables that are covered by the EFI spec and/or affect
the boot flow.

Signed-off-by: Ard Biesheuvel <[email protected]>

drivers/firmware/efi/efi.c

@@ -899,6 +899,7 @@ int efi_status_to_err(efi_status_t status)
 
 	return err;
 }
+EXPORT_SYMBOL_GPL(efi_status_to_err);
 
 static DEFINE_SPINLOCK(efi_mem_reserve_persistent_lock);
 static struct linux_efi_memreserve *efi_memreserve_root __ro_after_init;