sandbox: Increase the pre-relocation memory

This is close to full now, so increase it to avoid problems with adding
more devices.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/Kconfig b/Kconfig
index 42672a9..9e0b8af4 100644
--- a/Kconfig
+++ b/Kconfig
@@ -126,6 +126,7 @@
 config SYS_MALLOC_F
 	bool "Enable malloc() pool before relocation"
 	default y if DM
+
 	help
 	  Before relocation, memory is very limited on many platforms. Still,
 	  we can provide a small malloc() pool if needed. Driver model in
@@ -136,6 +137,7 @@
 	hex "Size of malloc() pool before relocation"
 	depends on SYS_MALLOC_F
 	default 0x1000 if AM33XX
+	default 0x2800 if SANDBOX
 	default 0x400
 	help
 	  Before relocation, memory is very limited on many platforms. Still,