eficonfig: menu-driven addition of UEFI boot option

This commit add the "eficonfig" command.
The "eficonfig" command implements the menu-driven UEFI boot option
maintenance feature. This commit implements the addition of
new boot option. User can select the block device volume having
efi_simple_file_system_protocol and select the file corresponding
to the Boot#### variable. User can also enter the description and
optional_data of the BOOT#### variable in utf8.

This commit adds "include/efi_config.h", it contains the common
definition to be used from other menus such as UEFI Secure Boot
key management.

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