rockchip: set Pre-reloc malloc pool size to 4kb for rk3368 based boards

The default 1kb pre-reloc malloc pool is not enough for dm
core to enable the dm-pre-reloc device drivers.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/sheep-rk3368_defconfig b/configs/sheep-rk3368_defconfig
index be00fad..da6b93a 100644
--- a/configs/sheep-rk3368_defconfig
+++ b/configs/sheep-rk3368_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_ARCH_ROCKCHIP=y
+CONFIG_SYS_MALLOC_F_LEN=0x1000
 CONFIG_ROCKCHIP_RK3368=y
 CONFIG_DEFAULT_DEVICE_TREE="rk3368-sheep"
 CONFIG_DEBUG_UART=y