drivers: spi: nrfx: Add support for SPIS3

This patch adds missing SPI_3_NRF_SPIS Kconfig option (referenced by
`ext/hal/nordic/nrfx_config_nrf9160.h`, although not defined anywhere)
and adds support for SPIS3 instance in the nrfx_spis driver shim.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>

drivers/spi/Kconfig.nrfx

@@ -162,13 +162,29 @@ endif # SPI_2
 
 if SPI_3
 
+choice
+	prompt "SPI Port 3 Driver type"
+
 config SPI_3_NRF_SPIM
-	bool
+	bool "nRF SPIM 3"
 	depends on HAS_HW_NRF_SPIM3
 	select NRFX_SPIM
-	default y
+	help
+	  Enable nRF SPI Master with EasyDMA on port 3.
 
-if SPI_3_NRF_SPIM
+config SPI_3_NRF_SPIS
+	bool "nRF SPIS 3"
+	depends on HAS_HW_NRF_SPIS3
+	depends on SPI_SLAVE
+	select NRFX_SPIS
+	help
+	  Enable nRF SPI Slave with EasyDMA on port 3.
+	  Due to hardware limitations the implementation supports only simple
+	  buffers (consisting of one part) located in RAM.
+
+endchoice
+
+if SPI_3_NRF_SPIM || SPI_3_NRF_SPIS
 
 config SPI_3_NRF_ORC
 	hex "Over-read Character"
@@ -178,8 +194,11 @@ config SPI_3_NRF_ORC
 	  Over-read character. Character clocked out after an over-read
 	  of the transmit buffer.
 
+endif # SPI_3_NRF_SPIM || SPI_3_NRF_SPIS
+
 config SPI_3_NRF_RX_DELAY
 	int "MISO sampling delay"
+	depends on SPI_3_NRF_SPIM && SOC_NRF52840
 	range 0 7
 	default 2
 	help
@@ -187,8 +206,6 @@ config SPI_3_NRF_RX_DELAY
 	  edge of SCK (leading or trailing, depending on the CPHA setting used)
 	  until the input serial data on MISO is actually sampled.
 
-endif # SPI_3_NRF_SPIM
-
 endif # SPI_3
 
 if NRFX_SPIM

drivers/spi/spi_nrfx_spis.c

@@ -295,3 +295,7 @@ SPI_NRFX_SPIS_DEVICE(1);
 #ifdef CONFIG_SPI_2_NRF_SPIS
 SPI_NRFX_SPIS_DEVICE(2);
 #endif
+
+#ifdef CONFIG_SPI_3_NRF_SPIS
+SPI_NRFX_SPIS_DEVICE(3);
+#endif