video console: move vidconsole_get_font_size() logic to driver ops

Since multiple vidconsole drivers exists, vidconsole_get_font_size()
implementation cannot longer live in vidconsole_uclass.c file.

Move current vidconsole_get_font_size logic to truetype driver ops.

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>