Convert CONFIG_SPL_DRIVERS_MISC_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/T4160QDS_NAND_defconfig b/configs/T4160QDS_NAND_defconfig
index d0793eb..f55f419 100644
--- a/configs/T4160QDS_NAND_defconfig
+++ b/configs/T4160QDS_NAND_defconfig
@@ -8,6 +8,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="PPC_T4160,RAMBOOT_PBL,SPL_FSL_PBL,NAND"
 CONFIG_BOOTDELAY=10
 CONFIG_SPL=y
+CONFIG_SPL_DRIVERS_MISC_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_MMC=y