tile regs: add defs and decoder for tile width/height
renderer: add 8x8 tile mode

This is an ad-hoc solution to quickly get 8x8 capability.  It is not
intended to be a long-term feature.  It should be replaced by the HSIZE
and VSIZE settings in the TILE_CTRL1 register.
renderer: Remove NUM_SPRITES define

It's defined in a header file.
renderer: Enable 8-bit tile map values

Enable option to read tile map as an array of 8-bit values rather than
16-bit values.  This is useful for rendering strings.