Convert CONFIG_SPL_DMA_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/am57xx_evm_nodt_defconfig b/configs/am57xx_evm_nodt_defconfig
index 0066691..93c0f59 100644
--- a/configs/am57xx_evm_nodt_defconfig
+++ b/configs/am57xx_evm_nodt_defconfig
@@ -1,8 +1,9 @@
 CONFIG_ARM=y
 CONFIG_OMAP54XX=y
 CONFIG_TARGET_AM57XX_EVM=y
-CONFIG_SPL=y
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
+CONFIG_SPL_DMA_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set