Use awk on runtime to get board info

Previously we prebuild boards.mk from boards.list using python.
Now we use few awk scripts bundled in boards.mk to get data from boards.list.

Pros:
 * Data is only in single file
 * In future, boards.list can be updated seperately or even downloaded from internet.

Cons:
 * Small runtime overhead
 * Awk script bundled with makefile
Install makefiles without execute bit.
Use yaamake_stages to evaluate variables before targets