Convert CONFIG_SPL_OMAP3_ID_NAND to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_OMAP3_ID_NAND

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-omap2/omap3/Kconfig b/arch/arm/mach-omap2/omap3/Kconfig
index 7b298d6..b90cade 100644
--- a/arch/arm/mach-omap2/omap3/Kconfig
+++ b/arch/arm/mach-omap2/omap3/Kconfig
@@ -149,6 +149,12 @@
 
 endchoice
 
+config SPL_OMAP3_ID_NAND
+	bool "Support OMAP3-specific ID and MFR function"
+	help
+	  Support for an OMAP3-specific set of functions to return the
+	  ID and MFR of the first attached NAND chip, if present.
+
 config SYS_SOC
 	default "omap3"