eficonfig: refactor eficonfig_process_common function

eficonfig: refactor eficonfig_process_common function

Current change boot order implementation does not call
eficonfig_process_common() and call own menu functions
for display_statusline, item_data_print and item_choice.
Change boot order functionality should call
eficonfig_process_common() to improve maintenanceability.

This commit is a preparation to remove the change boot
order specific implementation. The menu functions
(display_statusline, item_data_print and item_choice) are
added as argument of eficonfig_process_common().
The menu description string displayed at the bottom of
the menu is also added as argument.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>