Convert CONFIG_SPL_ENV_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/ti/am335x/Kconfig b/board/ti/am335x/Kconfig
index 97374bd..0a0cbf6 100644
--- a/board/ti/am335x/Kconfig
+++ b/board/ti/am335x/Kconfig
@@ -1,5 +1,8 @@
 if TARGET_AM335X_EVM
 
+config SPL_ENV_SUPPORT
+	default y
+
 config SYS_BOARD
 	default "am335x"
 
diff --git a/board/ti/common/Kconfig b/board/ti/common/Kconfig
index adf73ab..77c92a1 100644
--- a/board/ti/common/Kconfig
+++ b/board/ti/common/Kconfig
@@ -1,3 +1,6 @@
+config SPL_ENV_SUPPORT
+	default y
+
 config TI_I2C_BOARD_DETECT
 	bool "Support for Board detection for TI platforms"
 	help