spi: Fix types of the last chip select storage variables

First of all, last_cs_index_mask should be aligned with the original
cs_index_mask, which is 16-bit (for now) wide. Use the same pattern
for the last_cs_index_mask.

Second, last_cs can be negative and since 'char' is equal to 'unsigned
char' in the kernel, it's incorrect, strictly speaking, to assign
signed number to it. Use s8 type as it's done for *_native_cs ones.

With this change, regroup a bit the ordering to avoid too much memory
space to be wasted due to paddings. Shuffle kernel documentation
accordignly.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://msgid.link/r/20240307150256.3789138-3-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi.h

@@ -450,9 +450,11 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  *	the @cur_msg_completion. This flag is used to signal the context that
  *	is running spi_finalize_current_message() that it needs to complete()
  * @cur_msg_mapped: message has been mapped for DMA
+ * @fallback: fallback to PIO if DMA transfer return failure with
+ *	SPI_TRANS_FAIL_NO_START.
+ * @last_cs_mode_high: was (mode & SPI_CS_HIGH) true on the last call to set_cs.
  * @last_cs: the last chip_select that is recorded by set_cs, -1 on non chip
  *           selected
- * @last_cs_mode_high: was (mode & SPI_CS_HIGH) true on the last call to set_cs.
  * @xfer_completion: used by core transfer_one_message()
  * @busy: message pump is busy
  * @running: message pump is running
@@ -529,8 +531,6 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  *	If the driver does not set this, the SPI core takes the snapshot as
  *	close to the driver hand-over as possible.
  * @irq_flags: Interrupt enable state during PTP system timestamping
- * @fallback: fallback to PIO if DMA transfer return failure with
- *	SPI_TRANS_FAIL_NO_START.
  * @queue_empty: signal green light for opportunistically skipping the queue
  *	for spi_sync transfers.
  * @must_async: disable all fast paths in the core
@@ -710,10 +710,10 @@ struct spi_controller {
 	bool				rt;
 	bool				auto_runtime_pm;
 	bool				cur_msg_mapped;
-	char				last_cs[SPI_CS_CNT_MAX];
-	char				last_cs_index_mask;
-	bool				last_cs_mode_high;
 	bool                            fallback;
+	bool				last_cs_mode_high;
+	s8				last_cs[SPI_CS_CNT_MAX];
+	u32				last_cs_index_mask : SPI_CS_CNT_MAX;
 	struct completion               xfer_completion;
 	size_t				max_dma_len;