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>
3 files changed