Convert CONFIG_CMD_BLOB to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_BLOB

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Add imply CMD_BLOB under CHAIN_OF_TRUST]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Makefile b/cmd/Makefile
index 97c862f..e987868 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -152,9 +152,9 @@
 # Power
 obj-$(CONFIG_CMD_PMIC) += pmic.o
 obj-$(CONFIG_CMD_REGULATOR) += regulator.o
-endif # !CONFIG_SPL_BUILD
 
 obj-$(CONFIG_CMD_BLOB) += blob.o
+endif # !CONFIG_SPL_BUILD
 
 # core command
 obj-y += nvedit.o