Optimize Arduboy screen draw for ST7586.cpp

// should really use various NOPs here instead of while loop
#define SPOUT(x) SPDR = x; \
        while (!(SPSR & _BV(SPIF))) { }

// should really use various NOPs here instead of while loop
#define SPOUT2(x) SPDR = x; \
        while (!(SPSR & _BV(SPIF))) { }

// should really use various NOPs here instead of while loop
#define SPOUT3(x) SPDR = x; \
        while (!(SPSR & _BV(SPIF))) { }


// For reference, this is the "closed loop" C++ version of paintScreen()
// used prior to the above version.
void Arduboy2Core::paintScreen(uint8_t image[], bool clear)
{
  if (clear)
    {
      blank();
      return;
    }

  uint8_t *buffr;
  uint8_t x, y, data;
       
  sendLCDCommand(0x2B); // Row Address Setting (height)
  sendLCDData(0x00); // COM0 -> COM160
  sendLCDData(0x00); //
  sendLCDData(0x00); //
  sendLCDData(HEIGHT-1); //HEIGHT-1

  for (x=0; x<WIDTH; x++) {
    // start at x column of page 0
    buffr = &image + x;
    sendLCDCommand(0x2A); // Column Address Setting
    sendLCDData(0x00);
    sendLCDData(x);
    sendLCDData(0x00);
    sendLCDData(x);
    sendLCDCommand(0x2C); // write memory

    // iteratate over 8 vertical pages of SSD1306 hardware vertially
    for (y=8; y>0; y--) {
      data = *buffr;
      // 3 pixels horizontally, 2 pixels vertically
      // PURPOSSELY unrolling this loop
      if (data & 0b00000001) { SPOUT(0xFF); SPOUT2(0xFF); // #1
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b00000010) { SPOUT(0xFF); SPOUT2(0xFF); // #2
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b00000100) { SPOUT(0xFF); SPOUT2(0xFF); // #3
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b00001000) { SPOUT(0xFF); SPOUT2(0xFF); // #4
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b00010000) { SPOUT(0xFF); SPOUT2(0xFF); // #5
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b00100000) { SPOUT(0xFF); SPOUT2(0xFF); // #6
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b01000000) { SPOUT(0xFF); SPOUT2(0xFF); // #7
      } else { SPOUT(0); SPOUT2(0); }
      if (data & 0b10000000) { SPOUT(0xFF); SPOUT3(0xFF); // #8
      } else { SPOUT(0); SPOUT3(0); }
      buffr += 128; // skip to next page
    }
  }
}