drivers: mspi: Add the new MSPI API

The MSPI(multi-bit SPI) is provided as a generic API to accommodate
advanced SPI peripherals and devices that typically require command,
address and data phases, and multiple signal lines during these phases.
While the API supports advanced features such as XIP eXecute In Place
and scrambling, it is also compatible with generic SPI.

Signed-off-by: Swift Tian <swift.tian@ambiq.com>