spi: remove struct spi_message::is_dma_mapped

There are no more users of the deprecated is_dma_mapped in struct
spi_message so it can be removed.

References in documentation and comments are also removed.

A few similar checks if xfer->tx_dma or xfer->rx_dma are not NULL are
also removed since these are now guaranteed to be NULL because they
were previously set only if is_dma_mapped was true.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://msgid.link/r/20240325-spi-remove-is_dma_mapped-v2-1-d08d62b61f1c@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/spi/pxa2xx.rst

@@ -194,9 +194,6 @@ The following logic is used to determine the type of I/O to be used on
 a per "spi_transfer" basis::
 
   if spi_message.len > 65536 then
-	if spi_message.is_dma_mapped or rx_dma_buf != 0 or tx_dma_buf != 0 then
-		reject premapped transfers
-
 	print "rate limited" warning
 	use PIO transfers
 

Documentation/spi/spi-summary.rst

@@ -419,10 +419,6 @@ any more such messages.
     to make extra copies unless the hardware requires it (e.g. working
     around hardware errata that force the use of bounce buffering).
 
-    If standard dma_map_single() handling of these buffers is inappropriate,
-    you can use spi_message.is_dma_mapped to tell the controller driver
-    that you've already provided the relevant DMA addresses.
-
   - The basic I/O primitive is spi_async().  Async requests may be
     issued in any context (irq handler, task, etc) and completion
     is reported using a callback provided with the message.