spi: gxp_spi: Add GXP SPI controller driver

The GXP supports 3 separate SPI interfaces to accommodate the system
flash, core flash, and other functions. The SPI engine supports variable
clock frequency, selectable 3-byte or 4-byte addressing and a
configurable x1, x2, and x4 command/address/data modes. The memory
buffer for reading and writing ranges between 256 bytes and 8KB. This
driver supports access to the core flash.

Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index a1e515c..e48d72d 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -186,6 +186,12 @@
 	  Enable the Freescale QSPI driver to use full AHB memory map space for
 	  flash access.
 
+config GXP_SPI
+	bool "SPI driver for GXP"
+	imply SPI_FLASH_BAR
+	help
+	  Enable support for SPI on GXP.
+
 config ICH_SPI
 	bool "Intel ICH SPI driver"
 	help