spl: make SPL and normal u-boot stage use independent SYS_MALLOC_F_LEN

Some platforms have very limited SRAM to run SPL code, so there may
not be the same amount space for a malloc pool before relocation in
the SPL stage as the normal U-Boot stage.

Make SPL and (the full) U-Boot stage use independent SYS_MALLOC_F_LEN,
so the size of pre-relocation malloc pool can be configured memory
space independently.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
[fixed up commit-message:]
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/Kconfig b/Kconfig
index bb80ada..c1451bc 100644
--- a/Kconfig
+++ b/Kconfig
@@ -95,6 +95,16 @@
 	  particular needs this to operate, so that it can allocate the
 	  initial serial device and any others that are needed.
 
+config SPL_SYS_MALLOC_F_LEN
+        hex "Size of malloc() pool in spl before relocation"
+        depends on SYS_MALLOC_F
+        default SYS_MALLOC_F_LEN
+        help
+          Before relocation, memory is very limited on many platforms. Still,
+          we can provide a small malloc() pool if needed. Driver model in
+          particular needs this to operate, so that it can allocate the
+          initial serial device and any others that are needed.
+
 menuconfig EXPERT
 	bool "Configure standard U-Boot features (expert users)"
 	default y