Circle appears to fail on official touchscreen with older controller boards

[SteveSpencer]

Using an older "Official Touchscreen" with a Pi3B (32-bit arch) the backlight is not correctly set by the normal boot sequence. This leaves the display appearing blank, although it is displaying correctly.

I have tested this with two touchscreens and two different Pi3Bs, (four "platforms" in all), and this appears to be consistent. Through serial logging I was able to determine that the hardware was being initialised, the touchscreen was available (as touch1) and that it was reporting touch events as expected.

I modified a sample kernel.cpp to include explicit setting of the backlight value, and this resolved the problem.

By extending CKernelOptions and making a small change to CBcmFrameBuffer, I was able to then implement a cmdline.txt solution where the user can set the initial backlight level to a specific value.

Would there be interest in putting these changes into Circle generally?