Makefile: Simplify it and use variables

The targets were explicitly listed and had separate make commands for
each of the directories which could be combined into one. Putting the
directories in a common variable will also help to implement 'flawfinder'
and 'cppcheck' at later stages.

Signed-off-by: Vaibhav Gupta <vaibhav.gupta@cern.ch>

Makefile

 # SPDX-License-Identifier: CC0-1.0
 #
 # SPDX-FileCopyrightText: 2019 CERN
+C_DIRS = \
+     tools \
+     drivers/fmc
 
-all: modules tools
+DIRS = $(C_DIRS) \
+     Documentation/fmc
 
-tools:
-	@$(MAKE) -C tools all
+all clean cleanall install: $(DIRS)
 
 modules modules_install:
 	@$(MAKE) -C drivers/fmc/ $@
 
-sources srpm:
-	@$(MAKE) -C distribution $@
-
-clean:
-	@$(MAKE) -C distribution $@
-	@$(MAKE) -C drivers/fmc/ $@
-	@$(MAKE) -C tools $@
-
 cppcheck:
 	@$(MAKE) -C tools $@