SW: Greybus for Zephyr updates

[jadonk]

https://elinux.org/BeagleBoard/GSoC/Ideas-2022#Greybus_for_Zephyr_Updates

https://elinux.org/BeagleBoard/GSoC/2022_Proposal/GreybusforZephyrUpdates

Support all the relevant peripherals(SPI, UART, PWM, ADC, GPIO IRQ) on BeagleConnect Freedom on Greybus for Zephyr, this requires adding platform specific changes to enable the protocols and interface to the existing NuttX sources, once the protocols are tested over greybus-for-zephyr, the mikrobus kernel driver needs to be updated to be able to support mikrobus add-on boards on these buses. An ideal end goal for the project would be to test one mikrobus add-on board of each category over greybus with the corresponding device driver in kernel.