hw/display/artist: Allow screen size up to 2048 lines

hw/display/artist: Allow screen size up to 2048 lines

Adjust the ADDR_TO_Y() macro to extract 11 bits, which allows userspace
to address screen sizes up to 2048 lines (instead of 1024 before).

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>