RAK4260 SPI pin assignment

Issue: external SPI pin names are not consistent with R34 pin mapping capability.

Hello. RAK4260 has four external pins bundled into SPI port:

pin 22, SPI_MOSI - PA23, SERCOM5 PAD1
pin 23, SPI_CS - PA22, SERCOM5 PAD0
pin 23, SPI_CLK - PB23, SERCOM5 PAD3
pin 23, SPI_MISO - PB02, SERCOM5 PAD0

I believe there is a mistake in pin naming, because PINMUX feature of SERCOM5 does not permit MOSI to be assigned to PAD1 pin (see p560 of SAML21 datasheet). Using other combination (e.g. switching PB02 MOSI and PA23 MISO) appears feasible.

Handled in RAK4260 SPI Mux setup - #2 by carlrowan