Remove x.c dependency on term

The xinit function only needs to the rows/cols, so pass those in rather
than accessing term directly.  With a bit of arithmetic, we are able to
avoid the need for term.row and term.col in x2col, y2row, and
xdrawglyphfontspecs as well, completing the removal.

Term is now fully internal to st.c.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>