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/k2l_hs_evm_defconfig b/configs/k2l_hs_evm_defconfig
index 8f55836..a33313c 100644
--- a/configs/k2l_hs_evm_defconfig
+++ b/configs/k2l_hs_evm_defconfig
@@ -11,6 +11,7 @@
 CONFIG_TARGET_K2L_EVM=y
 CONFIG_ENV_SIZE=0x40000
 CONFIG_ENV_OFFSET=0x100000
+CONFIG_SYS_MALLOC_LEN=0x2000000
 CONFIG_DEFAULT_DEVICE_TREE="keystone-k2l-evm"
 CONFIG_FIT_IMAGE_POST_PROCESS=y
 CONFIG_OF_BOARD_SETUP=y