Convert CONFIG_SKIP_LOWLEVEL_INIT et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SKIP_LOWLEVEL_INIT
   CONFIG_SKIP_LOWLEVEL_INIT_ONLY

In order to do this, we need to introduce SPL and TPL variants of these
options so that we can clearly disable these options only in SPL in some
cases, and both instances in other cases.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/freescale/ls1021aqds/README b/board/freescale/ls1021aqds/README
index 6cf7146..e2ce001 100644
--- a/board/freescale/ls1021aqds/README
+++ b/board/freescale/ls1021aqds/README
@@ -113,6 +113,5 @@
 
 LS1021a rev1.0 Soc specific Options/Settings
 --------------------------------------------
-If the LS1021a Soc is rev1.0, you need modify the configure file.
-Add the following define in include/configs/ls1021aqds.h:
-#define CONFIG_SKIP_LOWLEVEL_INIT
+If the LS1021a Soc is rev1.0, you need modify the configuration and enable
+CONFIG_SPL_SKIP_LOWLEVEL_INIT in menuconfig or similar.
diff --git a/board/freescale/ls1021atwr/README b/board/freescale/ls1021atwr/README
index 896a659..a4639cd 100644
--- a/board/freescale/ls1021atwr/README
+++ b/board/freescale/ls1021atwr/README
@@ -110,6 +110,5 @@
 
 LS1021a rev1.0 Soc specific Options/Settings
 --------------------------------------------
-If the LS1021a Soc is rev1.0, you need modify the configure file.
-Add the following define in include/configs/ls1021atwr.h:
-#define CONFIG_SKIP_LOWLEVEL_INIT
+If the LS1021a Soc is rev1.0, you need modify the configuration and enable
+CONFIG_SPL_SKIP_LOWLEVEL_INIT in menuconfig or similar.