Convert CONFIG_SYS_MALLOC_LEN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MALLOC_LEN

Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/adp-ag101p_defconfig b/configs/adp-ag101p_defconfig
index 57348f0..c1cdb11 100644
--- a/configs/adp-ag101p_defconfig
+++ b/configs/adp-ag101p_defconfig
@@ -4,6 +4,7 @@
 CONFIG_NR_DRAM_BANKS=2
 CONFIG_ENV_SIZE=0x2000
 CONFIG_ENV_SECT_SIZE=0x20000
+CONFIG_SYS_MALLOC_LEN=0x80000
 CONFIG_DEFAULT_DEVICE_TREE="ag101p"
 CONFIG_TARGET_ADP_AG101P=y
 CONFIG_SYS_LOAD_ADDR=0x300000