nRF52: Rename pins to match nRF conventions and DK silk

[arturo182]

I think we should rename the pins to PX_YY instead of PAYY and PBYY, so we can match the naming used by Nordic and the silkscreen on the DKs, this issue was also discussed in #575 (comment)

If it's no problem, I can be assigned to this issue.

[microbuilder]

I'm OK with this personally.

[tannewt]

Sounds good to me!

[arturo182]

Fixed in #617

[microbuilder]

Thanks. Just waiting for the automated tests to run and I'll have a look at this.

[microbuilder]

Closed via #617