eficonfig: add "Change Boot Order" menu entry

This commit adds the menu entry to update UEFI BootOrder variable.
User moves the entry with UP/DOWN key, changes the order
with PLUS/MINUS key, press SPACE to activate or deactivate
the entry, then finalizes the order by ENTER key.
If the entry is activated, the boot index is added into the
BootOrder variable in the order of the list.

The U-Boot menu framework is well designed for static menu,
this commit implements the own menu display and key handling
for dynamically change the order of menu entry.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>