Fix NRF52 SPI pin initialization
Fix NRF52 SPI pin initialization

SPI pins are not initialized correctly according to the current
SPI mode.

This commit changes how the SPI instance is configured and ensures
that:

1. SPI pins are initialized on each object initialization.
2. SPI pins are reinitialized on each mode or object change.
3. SPI instance is only initialized when a change has occured.

mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,c1728p9/mbed-os,betzw/mbed-os,mbedmicro/mbed,mbedmicro/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,mbedmicro/mbed,betzw/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,andcor02/mbed-os,betzw/mbed-os,andcor02/mbed-os,andcor02/mbed-os,betzw/mbed-os,betzw/mbed-os,betzw/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,kjbracey-arm/mbed,mbedmicro/mbed