[SPI] add programmable chip-select operations

[stnolting]

This PR provides a rework of the SPI module.

• ✨ Add "programmable" chip-select enable(disable operations.
• ⚠️ Change layout of SPI control registers (CTRL) / not binary compatible to previous versions.
• ✔️ HAL functions remain unchanged / fully-backwards compatible.

Description

The chip-select lines of the SPI modules are not longer controlled by specific control register bits. Instead, these lines are controlled by new "commands" that are also written to the module's TX FIFO. Thus, entire SPI sequences can be programmed with any CPU interaction at all.

Example:

• Enable chip-select line 4 (write command to TX FIFO)
• Transmit N data bytes (write N data bytes to TX FIFO)
• Disable all chip-select lines (write command to TX FIFO)

So the entire SPI transmission can programmed as one block. The CPU is free to do other work while the SPI module in handling chip-select enable/disable and data transmission. Optionally, an IRQ can be triggered when the SPI module has completed the "programmed" transfer.