SPI API updates (3-wire, frame-format and extended modes)

[tbursztyka]

This is the main issue for adding new features to the existing SPI API.

• [x] Adding 3-wire support (half/full duplex modes) See #38386
• [x] Adding frame format selection (TI vs Motorola) See #39990
• [ ] Adding proper support for dual/quad/octal modes See #39991
• [x] Change cs_lock/lock_on and spi_release() See #40170
• [ ] Constify struct spi_config (API and all instances). API is still set to use constant struct spi_config, but let's verify that all instances are constant as well
• [ ] Updating DTS bindings to expose these new features (this probably needs to be done in the relevant PRs above)
• [x] Improving asynchronous methods See #43102

[jefflongo]

38386 added support for a SPI_HALF_DUPLEX option for 3-wire SPI mode. As far as I can tell, none of the platform SPI drivers use this yet. How is this flag meant to be used given that the API only exposes only a transceive function (i.e. deciding direction, switching direction)?