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/configs/P2020RDB-PC_36BIT_NAND_defconfig b/configs/P2020RDB-PC_36BIT_NAND_defconfig
index a2e0e9f..d6f3fb2 100644
--- a/configs/P2020RDB-PC_36BIT_NAND_defconfig
+++ b/configs/P2020RDB-PC_36BIT_NAND_defconfig
@@ -30,6 +30,8 @@
 # CONFIG_MISC_INIT_R is not set
 # CONFIG_SPL_FRAMEWORK is not set
 CONFIG_SPL_NAND_BOOT=y
+CONFIG_SPL_INIT_MINIMAL=y
+CONFIG_SPL_FLUSH_IMAGE=y
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_TPL=y
 CONFIG_TPL_ENV_SUPPORT=y