Fix analog ghosting

[RaceMiata]

Analog input ghosting is caused by TP2825 analog processor output voltage too high. To fix or at least mitigate the issue, the AGC (register 0x25) gain can be raised to prevent clipping. TP2825 registers 0x11 and 0x12 containing brightness and contrast values are also tweaked to match resulting range for digital input.

Also the contrast range of 47 in the goggle menu does not use up the full range for the FPGA register so a conversion was made map the full range of the slider to the full range (0-255) applicable.

[RaceMiata]

The previous workaround to mitigate ghosting by limiting brightness/contrast to 7/14 has now been removed. While this Pull Request significantly reduces ghosting for high brightness/contrast settings, it's still possible to have to set too high brightness/contrast from the menu to cause ghosting. Please use caution when setting brightness/contrast.

[RaceMiata]

This fix involves TP2825's AGC to "compress" dark vs bright images to prevent clipping with bright pixels. A couple scenarios may introduce artifacts:

1. image brighter than OSD elements may cause extra whole-scene dimming than it's already doing
2. super dark overall scene (e.g. Betaflight Race Pro menu with full black background) will show gray background

AGC (register 0x25) can be tuned (along with brightness/contrast registers 0x10/0x11) to trade-off between ghosting and AGC artifacts. Feedback from testers is welcome. Also any insight from the TP2825 specs or docs, @ligenxxxx or anybody else?

[ligenxxxx]

@RaceMiata Reg25[6:0] These bits determine the standard sync pulse amplitude for AGC reference.