build: Rework patch mechanism for Fuel submodules

build: Rework patch mechanism for Fuel submodules

While refactoring the patching mechanism, take care of:
- Sync submodule handling with Fuel@OPFNV;
- build: Investigate/prepare for moving patches to Fuel@OPNFV;
- build: Investigate divergent fuel-mirror;
- ISO build: cacheid for Fuel comps should not depend on
  Armband git commit;

CHANGE:
 Rename/shuffle patches while grouping them in "features",
 preparing for upstreaming them to Fuel@OPNFV and beyond.

CHANGE:
 Allow linking patches for better representing the dependency
 between one patch and different features.
 e.g. 0001-Add-arch-to-nailgun-release-and-target-image.patch:
   - part of `multiarch-fuel`, because it extends Fuel;
   - part of `direct-kernel-boot`, as arch is required for that;
   - part of `cross-bootstrap`, target image is arch-dependent;
 NOTE: Patch links are not staged to Fuel@OPNFV, they only serve
 as markers that a specific patch is part of a feature.

CHANGE:
 Kill all Fuel component submodules, now handled in Fuel@OPNFV:
  - fuel-agent
  - fuel-astute
  - fuel-library
  - fuel-mirror
  - fuel-nailgun-agent
  - fuel-web

CHANGE:
 Move armband-fuel-config.mk to armband git root.

FIXME: m1.micro-Increase-profile-RAM-size-to-128MB.patch is NOT
 part of `cross-bootstrap` feature, but patch context says so ...

FIXME: 0001-Add-arm64-deb-repositories-setup.patch is broken at
 `make patches-export` by removing spaces at EOL.

v2 -> v3:
 * Phony patch support (links to show a patch belongs to a feature);
 * Updated README.md
v3 -> v7:
 * Re-export Fuel submodules & plugins patches (update patch context);
 * Update Cavium mail addresses (s/caviumnetworks.com/cavium.com/);
 * Ignore submodule changes;
 * Add armband git repo info to gitinfo_fuel.txt at build time;

Implements: ARMBAND-136
Closes-bug: ARMBAND-95
Closes-bug: ARMBAND-93
Closes-bug: ARMBAND-92

Change-Id: I1a236d9f43b2e6dca22055911f696b43c22b5973
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>