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/integratorap_cm920t_defconfig b/configs/integratorap_cm920t_defconfig
index 1982a1b..a171895 100644
--- a/configs/integratorap_cm920t_defconfig
+++ b/configs/integratorap_cm920t_defconfig
@@ -6,6 +6,7 @@
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_ENV_SIZE=0x8000
 CONFIG_SYS_LOAD_ADDR=0x7fc0
+CONFIG_SYS_MALLOC_LEN=0x28000
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/mtdblock0 console=ttyAM0 console=tty"
 # CONFIG_DISPLAY_CPUINFO is not set