Convert CONFIG_SYS_NAND_SPL_KERNEL_OFFS to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_SPL_KERNEL_OFFS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/imx6q_logic_defconfig b/configs/imx6q_logic_defconfig
index cc7a6f0..df4c1c1 100644
--- a/configs/imx6q_logic_defconfig
+++ b/configs/imx6q_logic_defconfig
@@ -35,6 +35,7 @@
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SYS_SPL_ARGS_ADDR=0x18000000
+CONFIG_SYS_NAND_SPL_KERNEL_OFFS=0x500000
 CONFIG_SPL_FALCON_BOOT_MMCSD=y
 CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR=0x1000
 CONFIG_SPL_USB_HOST=y