Makefile: Individualize help targets & set as non-compile targets

- Including the help targets in the list of NOCOMPILE targets means they
can run even if the toolchain is mucked up.  Since they contain info on
building the toolchin, this is useful.
- Separate the three current parts of the help target into individual
components: help_coreboot, help_toolchain, and help_kconfig.  This is
mostly for the help_toolchin target which will be printed out by
toolchain.inc.

Change-Id: I365d95fd63e22bddd122fb1fede6f04270e03d63
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12542
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

Makefile.inc

@@ -477,8 +477,8 @@ gitconfig:
 	git config remote.origin.push HEAD:refs/for/master
 	(git config --global user.name >/dev/null && git config --global user.email >/dev/null) || (printf 'Please configure your name and email in git:\n\n git config --global user.name "Your Name Comes Here"\n git config --global user.email your.email@example.com\n'; exit 1)
 
-help::
-	@echo  '*** Toolchain ***'
+help_toolchain help::
+	@echo  '*** Toolchain targets ***'
 	@echo  '  crossgcc        - Build coreboot cross-compilers for all platforms'
 	@echo  '  crosstools      - Build coreboot cross-compiler and GDB for all platforms'
 	@echo  '  crossgcc-clean  - Remove all built coreboot cross-compilers'