altos: Restructure altos build to prepare for multi-arch support

Split out sources into separate directories:

	core:		architecture and product independent bits
	cc1111:		cc1111-specific code
	drivers:	architecture independent drivers
	product:	product-specific sources and Makefile fragments
	util:		scripts for building stuff

This should have no effect on the built products, but testing is encouraged

Signed-off-by: Keith Packard <keithp@keithp.com>