caif-driver: Add CAIF-SPI Protocol driver.

This patch introduces the CAIF SPI Protocol Driver for
CAIF Link Layer.

This driver implements a platform driver to accommodate for a
platform specific SPI device. A general platform driver is not
possible as there are no SPI Slave side Kernel API defined.
A sample CAIF SPI Platform device can be found in
.../Documentation/networking/caif/spi_porting.txt

Signed-off-by: Sjur Braendeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/caif/Kconfig

@@ -12,3 +12,22 @@ config CAIF_TTY
 	The CAIF TTY transport driver is a Line Discipline (ldisc)
 	identified as N_CAIF. When this ldisc is opened from user space
 	it will redirect the TTY's traffic into the CAIF stack.
+
+config CAIF_SPI_SLAVE
+	tristate "CAIF SPI transport driver for slave interface"
+	depends on CAIF
+	default n
+	---help---
+	The CAIF Link layer SPI Protocol driver for Slave SPI interface.
+	This driver implements a platform driver to accommodate for a
+	platform specific SPI device. A sample CAIF SPI Platform device is
+	provided in Documentation/networking/caif/spi_porting.txt
+
+config CAIF_SPI_SYNC
+	bool "Next command and length in start of frame"
+	depends on CAIF_SPI_SLAVE
+	default n
+	---help---
+	Putting the next command and length in the start of the frame can
+	help to synchronize to the next transfer in case of over or under-runs.
+	This option also needs to be enabled on the modem.