Added SUBARCH and test files/folder.

ARCH arm/lm4f120 now becomes ARCH=arm SUBARCH=lm4f120.
+ Calls to makefile also changed to mirror the new behaviour.

Config files now have CONFIG_TEST entries that will build files from
test/ folder and build for diferent SUBARCHs.
The rationale to build diferent sources for diferent MCUs
is: at this point we are dealing with real hardware most likely in
dev boards. Building this way let us specify buttons and leds to
function as interfaces and results of the tests.
Change formating to unix & renamed entry point.
arm/lm4f120: IRQ renaming and removal of GPIO6,7.