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/arch/powerpc/cpu/mpc8xxx/Makefile b/arch/powerpc/cpu/mpc8xxx/Makefile
index bec891d..e3a536d 100644
--- a/arch/powerpc/cpu/mpc8xxx/Makefile
+++ b/arch/powerpc/cpu/mpc8xxx/Makefile
@@ -5,10 +5,12 @@
 MINIMAL=
 
 ifdef CONFIG_SPL_BUILD
+ifndef CONFIG_TPL_BUILD
 ifdef CONFIG_SPL_INIT_MINIMAL
 MINIMAL=y
 endif
 endif
+endif
 
 ifdef MINIMAL