net/libertas: remove GPIO-CS handling in SPI interface code

This removes the dependency on GPIO framework and lets the SPI host
driver handle the chip select. The SPI host driver is required to keep
the CS active for the entire message unless cs_change says otherwise.
This patch collects the two/three single SPI transfers into a message.
Also the delay in read path in case use_dummy_writes are not used is
moved into the SPI host driver.

Tested-by: Mike Rapoport <mike@compulab.co.il>
Tested-by: Andrey Yurovsky <andrey@cozybit.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/Kconfig

@@ -153,7 +153,7 @@ config LIBERTAS_SDIO
 
 config LIBERTAS_SPI
 	tristate "Marvell Libertas 8686 SPI 802.11b/g cards"
-	depends on LIBERTAS && SPI && GENERIC_GPIO
+	depends on LIBERTAS && SPI
 	---help---
 	  A driver for Marvell Libertas 8686 SPI devices.