Make a new stucture struct efi_data to hold the info that describes
an efi variable. Make a common routine efi_open that opens the efi
variable file. Switch the efi get/set/del routines over to use
efi_open.
Signed-off-by: Geoff Levand <geoff@infradead.org> Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>