efi_loader: EFI_DEVICE_PATH_UTILITIES_PROTOCOL configurable

Allow the EFI_DEVICE_PATH_UTILITIES_PROTOCOL to be disabled via
configuration.

On systems that are very tight on U-Boot image size we may want to disable
the protocol. As it is required to run the UEFI Shell enable it by default.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>