efivars: parameterize efivars

Now that we all global variable state is encapsulated by struct efivars,
parameterize all functions to the efivars local to the control flow rather
than at file scope.  We do this by removing the variable "efivars" at file
scope and move its storage down to the end of the file.

Variables get at efivars by storing the efivars pointer within each
efivar_entry.  The "new_var" and "del_var" binary attribute files get at
the efivars through the private pointer.

Signed-off-by: Mike Waychison <mikew@google.com>
Cc: Matt Domsch <Matt_Domsch@dell.com>,
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>