Convert CONFIG_NAND_OMAP_ECCSCHEME to Kconfig

The values of CONFIG_NAND_OMAP_ECCSCHEME map to the enum in
include/linux/mtd/omap_gpmc.h for valid ECC schemes.  Make which one we
will use be a choice statement, enumerating the ones which we have
implemented.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am3517_evm_defconfig b/configs/am3517_evm_defconfig
index fa3c229..1bdebf5 100644
--- a/configs/am3517_evm_defconfig
+++ b/configs/am3517_evm_defconfig
@@ -57,6 +57,7 @@
 CONFIG_MMC_OMAP_HS=y
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y
+CONFIG_NAND_OMAP_ECCSCHEME_BCH8_CODE_HW_DETECTION_SW=y
 CONFIG_SYS_NAND_BLOCK_SIZE=0x20000
 CONFIG_SYS_NAND_PAGE_COUNT=0x40
 CONFIG_SYS_NAND_PAGE_SIZE=0x800