update feather_m4 bsp and examples to v2 as much as possible

[TDHolmes]

Wasn't too bad, mostly used feather_m0's transformation as a guide. I was able to test:

• blinky_basic
• dmac
• neopixel_rainbow
• pwm
• sleeping_timer_rtc
• timers
• trng
• usb_echo

I couldn't validate:

• uart
• uart_poll_echo
• serial

Unfortunately, sleeping_timer_rtc seems to not work. As that is my example, I'm going to take a look at this and see if I can fix it and/or if it's limited to M4

TODOs:

• someone validate the UART-y examples (not sure if we need to do this)
• figure out what's wrong with the sleeping_timer_rtc example - will figure this out in sleeping_timer_rtc examples don't work #488
• update to v2 SPI
• Wait on Add undocumented IOSet #506 to merge, then rebase onto that

[TDHolmes]

sleeping_timer_rtc also fails on feather_m0, so doesn't seem related to this refactor (that would've been shocking...)

[jbeaurivage]

@TDHolmes, thanks for working on this. I think the only thing I see missing is switching to spi::v2 in lib.rs.

[TDHolmes]

I just updated to v2 SPI, but I am not confident in the change I made to be honest. Looking at the data sheet, it seems like the SPI hookup used by the feather board shouldn't work. The IoSet doesn't seem to match up even though they all are on Sercom1.

PA17 Sclk - IoSet1
PB23 Mosi - IoSet3
PB22 Miso - IoSet3

I added IoSet3 as another option for PA17 on Sercom1. @jbeaurivage / @bradleyharden is it possible the data sheet just omitted this?

[bradleyharden]

I won't try auto merge for this. I expect there will be a conflict with #506. But it should be ready for merge

[TDHolmes]

I'll need to edit this a bit after rebasing. I'll ping ya when I do it later tonight

[bradleyharden]

Have you seen #445? Could you add that pin as well?

[TDHolmes]

@bradleyharden ah let me sneak that in

[TDHolmes]

@bradleyharden should be good to go!