add support for 32MHz crystal

[bearsh]

it looks like a 16MHz crystal is assumed and it's currently not possible to have it working for a 32MHz crystal...
what about adding something like YOTTA_CFG_HARDWARE_CLOCKS_NRF_HFCLK_SRC and then set the hf clock source in SystemInit()?
I suppose a special bootloader for 32MHz is needed as well...

[pan-]

Yes a special bootloader is needed.

It would be a good thing to build the bootloader instead of merging it. I think it will be necessary to properly resolve this defect.