[make][buildall] add ability to filter buildall by architecture

Clean up make targets list-arch and list-toolchain to be much faster and
work without needing to invoke the archtecture's arch rules.mk. This
should make it work on machines that do not have that particular
toolchain in the path.

This is setting up for using it in the github action script.

make/help.mk

@@ -12,9 +12,14 @@ help:
 	@echo "LK build system quick help"
 	@echo "Individual projects are built into a build-<project> directory"
 	@echo "Output binary is located at build-<project>/lk.bin"
+	@echo ""
 	@echo "Environment or command line variables controlling build:"
 	@echo "PROJECT = <project name>"
 	@echo "TOOLCHAIN_PREFIX = <absolute path to toolchain or relative path with prefix>"
+	@echo "WERROR = 1 : treat warnings as errors"
+	@echo "DEBUG = 0,1,2 : set debug level (0=NONE, 1=INFO, 2=DEBUG), default is 2"
+	@echo "BUILDDIR = <path to build directory> (default is build-<project>)"
+	@echo "BUILDDIR_SUFFIX = <suffix to add to build directory> (default is empty)"
 	@echo ""
 	@echo "Special make targets:"
 	@echo "make help: This help"
@@ -34,6 +39,9 @@ help:
 	@echo "make testproject clean"
 	@echo ""
 	@echo "output will be in build-testproject/"
+	@echo ""
+	@echo "Check the project/ directory for available projects"
+	@echo "and their rules.mk files for more information."
 
 endif