spi: Kconfig: Create ISSI Kconfig entry

Add ISSI to Kconfig to make it selectable via menuconfig.
Also convert all current platforms.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zc702_defconfig b/configs/zynq_zc702_defconfig
index dd5f834..bac538c 100644
--- a/configs/zynq_zc702_defconfig
+++ b/configs/zynq_zc702_defconfig
@@ -52,6 +52,7 @@
 CONFIG_MMC_SDHCI_ZYNQ=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
+CONFIG_SPI_FLASH_ISSI=y
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_SPI_FLASH_STMICRO=y