BBHandler: Improve IN_PYTHON_EOF handling

BBHandler: Improve IN_PYTHON_EOF handling

Now we're actively using the line numbers for other thins, having
magic values like IN_PYTHON_EOF causes problems, in particular, 32
bit overflow on 32 bit machines.

There is a neater way to signal eof to feeder(), just using an extra
parameter so use this instead and drop the IN_PYTHON_EOF magic values.

This has the added bonus that line numbers are then correct for
python functions at the end of files.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>