eficonfig: refactor file selection handling

eficonfig_select_file_handler() is commonly used to select the
file. eficonfig_display_select_file_option() adds an additional
menu to clear the selected file.
eficonfig_display_select_file_option() is not always necessary
for the file selection process, so it must be outside of
eficonfig_select_file_handler().

This commit also renames the following functions to avoid confusion.
 eficonfig_select_file_handler() -> eficonfig_process_select_file()
 eficonfig_select_file() -> eficonfig_show_file_selection()
 eficonfig_display_select_file_option() -> eficonfig_process_show_file_option()

Finally, test_eficonfig.py need to be updated to get aligned with
the above modification.

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

test/py/tests/test_eficonfig/test_eficonfig.py

@@ -352,6 +352,7 @@ def test_efi_eficonfig(u_boot_console, efi_eficonfig_data):
         press_up_down_enter_and_wait(0, 1, True, 'Quit')
         press_up_down_enter_and_wait(0, 0, True, 'No block device found!')
         press_escape_key(False)
+        press_escape_key(False)
         check_current_is_maintenance_menu()
         # Return to U-Boot console
         press_escape_key(True)