This change introduces a new SPI HAL API, featuring abstractions
enabling a target device to communicate with SPI peripherals in
a portable and consistent fashion.
Change-Id: Idc085c4727abb9247732c40cc84d05ee4113bd78
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/70140
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Mark Slevinsky <markslevinsky@google.com>
