dts: OF_HAS_PRIOR_STAGE should depend on !BLOBLIST

When BLOBLIST is enabled, FDT is expected to be from bloblist
carried from previous stage, instead of from OF_BOARD, therefore
only enable OF_HAS_PRIOR_STAGE when BLOBLIST is disabled.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
diff --git a/dts/Kconfig b/dts/Kconfig
index 00c0aef..def0e17 100644
--- a/dts/Kconfig
+++ b/dts/Kconfig
@@ -121,6 +121,7 @@
 
 config OF_HAS_PRIOR_STAGE
 	bool
+	depends on !BLOBLIST
 	help
 	  Indicates that a prior stage of the firmware (before U-Boot proper)
 	  makes use of device tree and this board normally boots with that prior