Except for architecture and processor names, buildroot uses capitalized
configuration names, so change the macro names for xtensa to follow that
standard.
Change the overlay file to have a subdirectory for each component
(gdb, binutils, gcc, etc.) to make it more future-prove.
Signed-off-by: Chris Zankel <chris@zankel.net>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>