Convert CONFIG_SPL_INIT_MINIMAL et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_INIT_MINIMAL
   CONFIG_SPL_FLUSH_IMAGE
   CONFIG_SPL_SKIP_RELOCATE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/congatec/common/Makefile b/board/congatec/common/Makefile
index d4ddfbf..2db0fc1 100644
--- a/board/congatec/common/Makefile
+++ b/board/congatec/common/Makefile
@@ -8,10 +8,12 @@
 MINIMAL=
 
 ifdef CONFIG_SPL_BUILD
+ifndef CONFIG_TPL_BUILD
 ifdef CONFIG_SPL_INIT_MINIMAL
 MINIMAL=y
 endif
 endif
+endif
 
 ifdef MINIMAL
 # necessary to create built-in.o