Avoid Official/Partner/Community differentiation: use same directory for all platforms/targets.

We initially wanted to provide different level of support for the platforms/targets, mainly
to avoid too much maintenance and let each contributor update its contributed platforms and
targets, but it's easier to update all platforms/targets all-together when LiteX evolves or
changes (and that's what has been done on litex-boards since the creation of the repository).
So let just simplify things and avoid this differentiation.

README

@@ -5,20 +5,8 @@
 
                        LiteX boards files
 
-              Copyright 2012-2019 / LiteX-Hub community
+              Copyright 2012-2020 / LiteX-Hub community
 
 [> Intro
 --------
 Supported boards files (platforms/targets) for LiteX.
-
-Official:
----------
-Platforms / Targets actively tested and included in the CI system.
-
-Partner:
--------
-Platforms / Targets supported by other groups/partners.
-
-Community:
-----------
-Platforms / Targets supported by the community in a "best effort" manner.

litex_boards/platforms.py

@@ -1,15 +0,0 @@
-import sys
-import importlib
-
-class Platforms:
-    def __getattr__(self, name):
-        if name == "__path__":
-            return []
-        for support in ["official", "partner", "community"]:
-            try:
-                return importlib.import_module("litex_boards." + support + ".platforms." + name)
-            except ModuleNotFoundError:
-                pass
-        raise ModuleNotFoundError
-
-sys.modules[__name__] = Platforms()

litex_boards/targets.py

@@ -1,15 +0,0 @@
-import sys
-import importlib
-
-class Targets:
-    def __getattr__(self, name):
-        if name == "__path__":
-            return []
-        for support in ["official", "partner", "community"]:
-            try:
-                return importlib.import_module("litex_boards." + support + ".targets." + name)
-            except ModuleNotFoundError:
-                pass
-        raise ModuleNotFoundError
-
-sys.modules[__name__] = Targets()