configs: meson64: permit redefining SYS_MALLOC_LEN

Permit redefining SYS_MALLOC_LEN for board specific configs.
This is especially useful for Android with AVB, which requires a malloc
length of 128M.

Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

include/configs/meson64.h

@@ -32,7 +32,9 @@
 #define CONFIG_CPU_ARMV8
 #define CONFIG_REMAKE_ELF
 #define CONFIG_SYS_MAXARGS		32
+#ifndef CONFIG_SYS_MALLOC_LEN
 #define CONFIG_SYS_MALLOC_LEN		(32 << 20)
+#endif
 #define CONFIG_SYS_CBSIZE		1024
 
 #define CONFIG_SYS_SDRAM_BASE		0