Make SDRAM properly consider num column/row parameters.  Some places still used hard coded constants.
Increase size of memory in FPGA sim.
Fix some VGA display issues:
- pixel_count increments by 16, but end of frame check was checking for NUM_PIXELS - 1.  As a result, it would just loop through all of memory instead of using the same framebuffer.
- A few off-by-ones in the vga_timing_generator.  Signal was starting one horizontal pixel late and displayed one scanline too many (which would cause the display to roll)