spl/nand: introduce CONFIG_SPL_NAND_DRIVERS, _BASE, and _ECC.

Some small SPLs do not use nand_base.c, and a subset of those also
require a special driver.  Some SPLs need software ECC but others can't
fit it.

All existing boards that specify CONFIG_SPL_NAND_SUPPORT have these
symbols added to preserve existing behavior.

Signed-off-by: Scott Wood <scottwood@freescale.com>
--
v2: use positive logic for including bits of NAND, rather than
a MINIMAL symbol that excludes things.
diff --git a/include/configs/cam_enc_4xx.h b/include/configs/cam_enc_4xx.h
index 56dc1cb..a7a698c 100644
--- a/include/configs/cam_enc_4xx.h
+++ b/include/configs/cam_enc_4xx.h
@@ -219,6 +219,9 @@
 #define CONFIG_SPL_BOARD_INIT
 #define CONFIG_SPL_LIBGENERIC_SUPPORT
 #define CONFIG_SPL_NAND_SUPPORT
+#define CONFIG_SPL_NAND_BASE
+#define CONFIG_SPL_NAND_DRIVERS
+#define CONFIG_SPL_NAND_ECC
 #define CONFIG_SPL_NAND_SIMPLE
 #define CONFIG_SYS_NAND_HW_ECC_OOBFIRST
 #define CONFIG_SPL_SERIAL_SUPPORT