Makefile.features: assert CPU has been defined by BOARD/Makefile.feat…

…ures

CPU must now be defined by `$(RIOTBOARD)/$(BOARD)/Makefile.features` or
one of its common included Makefile.features file.
The cpu `Makefile.dep` file can now automatically be included when it exists.

Makefile.dep

@@ -5,12 +5,8 @@ OLD_USEPKG := $(sort $(USEPKG))
 # include board dependencies
 -include $(RIOTBOARD)/$(BOARD)/Makefile.dep
 
-# Transitional conditional include until all boards define 'CPU' in
-# Makefile.features
-ifneq (,$(CPU))
-  # include cpu dependencies
-  -include $(RIOTCPU)/$(CPU)/Makefile.dep
-endif
+# include cpu dependencies
+-include $(RIOTCPU)/$(CPU)/Makefile.dep
 
 # include external modules dependencies
 # processed before RIOT ones to be evaluated before the 'default' rules.

Makefile.features

@@ -5,19 +5,15 @@
 # This makes them available when setting features based on CPU_MODEL in the cpu
 # Makefile.features and also during dependency resolution.
 
-# Transition:
-#   Moving 'CPU/CPU_MODEL' to Makefile.features is an ongoing work and may not
-#   reflect the state of all boards for the moment.
-
 include $(RIOTBOARD)/$(BOARD)/Makefile.features
 
-# Transitional conditional include until all boards define 'CPU'
-ifneq (,$(CPU))
-  include $(RIOTCPU)/$(CPU)/Makefile.features
-else
-  $(warning CPU must be defined by board / board_common Makefile.features)
+# Sanity check
+ifeq (,$(CPU))
+  $(error CPU must be defined by board / board_common Makefile.features)
 endif
 
+include $(RIOTCPU)/$(CPU)/Makefile.features
+
 
 # Resolve FEATURES_ variables
 # Their value will only be complete after resolving dependencies

Makefile.include

@@ -298,13 +298,6 @@ include $(RIOTBOARD)/$(BOARD)/Makefile.include
 INCLUDES += -I$(RIOTCPU)/$(CPU)/include
 include $(RIOTCPU)/$(CPU)/Makefile.include
 
-# Sanity check
-# The check is only done after 'include $(RIOTBOARD)/$(BOARD)/Makefile.include'
-# because we need to have the 'CPU' variable defined
-ifeq (,$(filter $(RIOTCPU)/$(CPU)/Makefile.features,$(MAKEFILE_LIST)))
-  $(error $$(RIOTCPU)/$$(CPU)/Makefile.features must have been included by the board / board common Makefile.features or Makefile.features)
-endif
-
 # Assume GCC/GNU as supported toolchain if CPU's Makefile.include doesn't
 # provide this macro
 TOOLCHAINS_SUPPORTED ?= gnu