Rockbox

Some Sansa Clip+ players don’t have a si4700 chip like many other AMS sansas, but some unidentified other SiLabs FM tuner chip.

This patch adds support for this chip. It uses the multiple tuner mechanism so I had to add detection code to decide between a si4700 or the mystery chip. This may have impact on other players using an si4700.

Things that do not work right yet:
- I’ve seen it get auto-scanned presets off by 1 channel (e.g. 0.1 MHz)
- Stereo indication is not supported yet
- It’s tricky to select the proper debug menu info, so it currently shows debug info for the si4700 only (even though the player may have detected the mystery FM chip).

Things to test:
- Verify that radio on sansa clip+ players with an si4700 still works
- Verify that radio on other players with an si4700 still works (AMS sansas, gigabeat S). It still works on my Clip v1.