bli: Add explicit dependency on the part_gpt module

bli: Add explicit dependency on the part_gpt module

The bli module has a "hidden" dependency on the part_gpt module, which
is not picked up automatically by the build system. One purpose of the
bli module is to communicate the GPT UUID of the partition GRUB was
launched from to Linux user-space (systemd-gpt-auto-generator).
Without the part_gpt module, bli is not able to obtain the UUID. Since
bli does its work in the module initialization function, the order in
which the modules are loaded is also important: part_gpt needs to be
loaded before the bli module.

To solve this, track this dependency explicitly.

Note that the Boot Loader Interface specification, which bli aims to
implement, requires GPT formatted drives. The bli module ignores all
other partition formats.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>