Migrate all applets to the generic clock/strobe generator

[whitequark]

This includes applets:

• [ ] audio-dac
• [x] audio-yamaha-opl
• [ ] debug-arm-swd
• [ ] display-hd44780
• [ ] display-pdi
• [ ] i2c-master
• [ ] jtag-probe
• [x] spi-master
• [ ] memory-floppy
• [ ] program-avr-spi
• [x] uart
• [ ] video-rgb-input

Important note: when the applet includes an FSM, it's necessary to adjust min_cyc to account for the maximum amount of FSM states, such that a strobe is never missed. This is pretty much the only tricky part of this.

[whitequark]

It can actually be quite annoying to do this, and it's less relevant with the SERDES+sideband design I would like to move towards. So I think perhaps it's only warranted to migrate to applet.derive_clock but not necessarily to the clock generator.