Makefiles: Add / Update help for makefile targets

Currently running 'make help' just gives help for the kconfig targets.

This adds help for common coreboot and toolchain targets.  It stops
printing some of the less common kconfig targets, but still leaves
them in the makefile as documentation.

Change-Id: I2a00fcbc06f05dc4029a91f3dff830c19e4d1329
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12458
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

Makefile

@@ -93,6 +93,21 @@ DOXYGEN_OUTPUT_DIR := doxygen
 
 all: real-all
 
+help::
+	@echo  '*** coreboot platform ***'
+	@echo  '  Use "make [target] V=1" for extra build debug information'
+	@echo  '  all                   - Build coreboot'
+	@echo  '  clean                 - Remove coreboot build artifacts'
+	@echo  '  distclean             - Remove build artifacts and config files'
+	@echo  '  doxygen               - Build doxygen documentation for coreboot'
+	@echo  '  what-jenkins-does     - Run platform build tests (Use CPUS=# for more cores)'
+	@echo  '  printall              - print makefile info for debugging'
+	@echo  '  lint / lint-stable    - run coreboot lint tools (all / minimal)'
+	@echo  '  gitconfig             - set up git to subnit patches to coreboot'
+	@echo  '  ctags / ctags-project - make ctags file for all of coreboot or current board'
+	@echo  '  cscope / cscope-project - make cscope.out file for coreboot or current board'
+	@echo
+
 # This include must come _before_ the pattern rules below!
 # Order _does_ matter for pattern rules.
 include $(srck)/Makefile