Axiado AX3000 SoC SPI DB controller driver

Axiado AX3000 SoC SPI DB controller driver

Merge series from Vladimir Moravcevic <vmoravcevic@axiado.com>:

This series introduces new SPI controller driver for Axiado AX3000 SoC
and its evaluation board.

The SPI controller provides:
- Full-duplex and half-duplex transfer support
- Configurable clock polarity and phase
- Interrupt-driven

Functionality has been verified using the `jedec,spi-nor` interface to
access onboard flash memory. This ensures compatibility with common NOR
flash devices used in boot and storage subsystem.

Further improvements, including performance tuning and extended hardware
feature support, will be submitted in follow-up patches.