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/armadillo-800eva_defconfig b/configs/armadillo-800eva_defconfig
index 903fd83..39e408e 100644
--- a/configs/armadillo-800eva_defconfig
+++ b/configs/armadillo-800eva_defconfig
@@ -7,6 +7,7 @@
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_ENV_SIZE=0x20000
 CONFIG_ENV_SECT_SIZE=0x20000
+CONFIG_SYS_MALLOC_LEN=0x100000
 CONFIG_ARCH_RMOBILE_BOARD_STRING="Armadillo-800EVA Board"
 CONFIG_R8A7740=y
 CONFIG_TARGET_ARMADILLO_800EVA=y