This moves the message state in the AXI SPI Engine driver to a new
struct spi_engine_msg_state.

Previously, the driver state contained various pointers that pointed
to memory owned by a struct spi_message. However, it did not set any of
these pointers to NULL when a message was completed. This could lead to
use after free bugs.

Example of how this could happen:
1. SPI core calls into spi_engine_transfer_one_message() with msg1.
2. Assume something was misconfigured and spi_engine_tx_next() is not
   called enough times in interrupt callbacks for msg1 such that
   spi_engine->tx_xfer is never set to NULL before the msg1 completes.
3. SYNC interrupt is received and spi_finalize_current_message() is
   called for msg1. spi_engine->msg is set to NULL but no other
   message-specific state is reset.
4. Caller that sent msg1 is notified of the completion and frees msg1
   and the associated xfers and tx/rx buffers.
4. SPI core calls into spi_engine_transfer_one_message() with msg2.
5. When spi_engine_tx_next() is called for msg2, spi_engine->tx_xfer is
   still be pointing to an xfer from msg1, which was already freed.
   spi_engine_xfer_next() tries to access xfer->transfer_list of one
   of the freed xfers and we get a segfault or undefined behavior.

To avoid issues like this, instead of putting per-message state in the
driver state struct, we can make use of the struct spi_message::state
field to store a pointer to a new struct spi_engine_msg_state. This way,
all of the state that belongs to specific message stays with that
message and we don't have to remember to manually reset all aspects of
the message state when a message is completed. Rather, a new state is
allocated for each message.

Most of the changes are just renames where the state is accessed. One
place where this wasn't straightforward was the sync_id member. This
has been changed to use ida_alloc_range() since we needed to separate
the per-message sync_id from the per-controller next available sync_id.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231117-axi-spi-engine-series-1-v1-9-cc59db999b87@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>