This makes it so that all a port needs to do is set the relevant variables
and "include extmod.mk" and doesn't need to worry about adding anything to
OBJ, CFLAGS, SRC_QSTR, etc.
Make all extmod variables (src, flags, etc) private to extmod.mk.
Also move common/shared, extmod-related fragments (e.g. wiznet, cyw43,
bluetooth) into extmod.mk.
Now that SRC_MOD, CFLAGS_MOD, CXXFLAGS_MOD are unused by both extmod.mk
(and user-C-modules in a previous commit), remove all uses of them from
port makefiles.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
d6d8722558