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/arch/nds32/cpu/n1213/ae3xx/lowlevel_init.S b/arch/nds32/cpu/n1213/ae3xx/lowlevel_init.S
index 507d79e..25ec185 100644
--- a/arch/nds32/cpu/n1213/ae3xx/lowlevel_init.S
+++ b/arch/nds32/cpu/n1213/ae3xx/lowlevel_init.S
@@ -94,7 +94,7 @@
 	move	  $lp, $r11
 	ret
 
-#ifndef CONFIG_SKIP_LOWLEVEL_INIT
+#if !CONFIG_IS_ENABLED(SKIP_LOWLEVEL_INIT)
 .globl	lowlevel_init
 lowlevel_init:
 	move	$r10, $lp
@@ -144,4 +144,4 @@
 	ret
 #endif
 
-#endif /* #ifndef CONFIG_SKIP_LOWLEVEL_INIT */
+#endif /* #if !CONFIG_IS_ENABLED(SKIP_LOWLEVEL_INIT) */
diff --git a/arch/nds32/cpu/n1213/ag101/lowlevel_init.S b/arch/nds32/cpu/n1213/ag101/lowlevel_init.S
index 73f1f52..ce5fefd 100644
--- a/arch/nds32/cpu/n1213/ag101/lowlevel_init.S
+++ b/arch/nds32/cpu/n1213/ag101/lowlevel_init.S
@@ -164,7 +164,7 @@
 	ret
 
 
-#ifndef CONFIG_SKIP_LOWLEVEL_INIT
+#if !CONFIG_IS_ENABLED(SKIP_LOWLEVEL_INIT)
 
 .globl	lowlevel_init
 lowlevel_init:
@@ -314,4 +314,4 @@
     li      $r8, (CONFIG_DEBUG_LED)
     swi     $r7, [$r8]
     ret
-#endif /* #ifndef CONFIG_SKIP_LOWLEVEL_INIT */
+#endif /* #if !CONFIG_IS_ENABLED(SKIP_LOWLEVEL_INIT) */
diff --git a/arch/nds32/cpu/n1213/start.S b/arch/nds32/cpu/n1213/start.S
index 3395721..f02508f 100644
--- a/arch/nds32/cpu/n1213/start.S
+++ b/arch/nds32/cpu/n1213/start.S
@@ -174,7 +174,7 @@
 
 	jal mem_init
 
-#ifndef CONFIG_SKIP_LOWLEVEL_INIT
+#if !CONFIG_IS_ENABLED(SKIP_LOWLEVEL_INIT)
 	jal	lowlevel_init
 /*
  *  gp = ~VMA          for burn mode