mips: spi: mscc: Add fast bitbang SPI driver

This patch add a new SPI driver for MSCC SOCs that does not sport the
designware SPI hardware controller.

Performance gain: 7.664 seconds vs. 17.633 for 1 Mbyte write.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index a7bb5b3..de4d62d 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -294,6 +294,13 @@
 	 Enable Soft SPI driver. This driver is to use GPIO simulate
 	 the SPI protocol.
 
+config MSCC_BB_SPI
+	bool "MSCC bitbang SPI driver"
+	depends on SOC_VCOREIII
+	help
+	  Enable MSCC bitbang SPI driver. This driver can be used on
+	  MSCC SOCs.
+
 config CF_SPI
 	bool "ColdFire SPI driver"
 	help