_set_size_and_colorspace: Boost pixel clock

Limor noticed that the pixel clock was very low, leading to a frame rate
of just 7.6Hz from the camera.  Because the structure of the parallel
capture driver means dropping at least half of all frames, this led to
a really low LCD refresh rate of just 3.8Hz.

Bump the PLL multiplier for non-JPEG modes from 8 to 32.  This gives
a capture framerate of about 30FPS and an LCD refresh rate of about 15Hz.

Going significantly higher (multiplier 48) gives a jumbled display, but even
going slightly higher doesn't have a big effect on frame rate because the total
LCD data transmission time of about 30ms starts to overlap with the next frame.
Increasing the multiplier to 40 increases the capture frame rate to 40Hz but
the LCD refresh rate decreaseds to just 13Hz, because only 1/3 of captured
frames are displayed instead of 1/2.  This is highly dependent on the LCD
resolution & speed.

Author: jepler

adafruit_ov5640.py

@@ -1065,7 +1065,7 @@ def _set_size_and_colorspace(self):  # pylint: disable=too-many-locals
                 sys_mul = 180
             self._set_pll(False, sys_mul, 4, 2, False, 2, True, 4)
         else:
-            self._set_pll(False, 8, 1, 1, False, 1, True, 4)
+            self._set_pll(False, 32, 1, 1, False, 1, True, 4)
 
         self._set_colorspace()