All the SPI initialization should be handled by us

[giuliomoro]

If the PRU has started before the spi-omap2-mcspi driver has loaded:

• analogs will not work
• you will hear sound till the driver does something(usually a split-second)
• then the PRU hangs on DAC_WAIT_FOR_FINISH

We should do all the spi init ourselves and get rid of the linux driver.

[giuliomoro]

You would get something like this in dmesg when the SPI driver loads after you started the PRU:

[12.829978] omap_hwmod: spi0: _wait_target_disable failed

https://github.com/BelaPlatform/bela-image-builder/issues/55