spl: Use CONFIG_SPL... instead of CONFIG_..._SPL_...

We like to put the SPL first so it is clear that it relates to SPL. Rename
various malloc-related options which have crept in, to stick to this
convention.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/Kconfig b/Kconfig
index 7b360ef..f576e03 100644
--- a/Kconfig
+++ b/Kconfig
@@ -308,7 +308,7 @@
 	  particular needs this to operate, so that it can allocate the
 	  initial serial device and any others that are needed.
 
-	  It is possible to enable CFG_SYS_SPL_MALLOC_START to start a new
+	  It is possible to enable CFG_SPL_SYS_MALLOC_START to start a new
 	  malloc() region in SDRAM once it is inited.
 
 config TPL_SYS_MALLOC_F_LEN