Convert CONFIG_MXC_NAND_HWECC to Kconfig

This converts the following to Kconfig:
   CONFIG_MXC_NAND_HWECC

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mtd/nand/raw/Kconfig b/drivers/mtd/nand/raw/Kconfig
index 25b829f..1e4e5c9 100644
--- a/drivers/mtd/nand/raw/Kconfig
+++ b/drivers/mtd/nand/raw/Kconfig
@@ -479,6 +479,10 @@
 	depends on NAND_MXC && SPL_NAND_SUPPORT
 	default 268435456
 
+config MXC_NAND_HWECC
+	bool "Hardware ECC support in MXC NAND"
+	depends on NAND_MXC
+
 config NAND_MXS
 	bool "MXS NAND support"
 	depends on MX23 || MX28 || MX6 || MX7 || IMX8 || IMX8M