Convert CONFIG_SPL_MUSB_NEW_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/am335x_boneblack_defconfig b/configs/am335x_boneblack_defconfig
index 0aaa27a..d2dfb30 100644
--- a/configs/am335x_boneblack_defconfig
+++ b/configs/am335x_boneblack_defconfig
@@ -6,6 +6,7 @@
 CONFIG_VERSION_VARIABLE=y
 CONFIG_SPL=y
 CONFIG_SPL_STACK_R=y
+CONFIG_SPL_MUSB_NEW_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Press SPACE to abort autoboot in %d seconds\n"