Convert CONFIG_SYS_MONITOR_LEN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MONITOR_LEN

To do this, we set a default of 0 for everyone because there are a
number of cases where we define CONFIG_SYS_MONITOR_LEN but the only
impact is that we set TOTAL_MALLOC_LEN to be CONFIG_SYS_MALLOC_LEN +
CONFIG_ENV_SIZE, so we must continue to allow all boards to set this
value. Update the SPL code to use 200 KB as the default raw U-Boot size
directly, if we don't have a real CONFIG_SYS_MONITOR_LEN value.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/eb_cpu5282_internal_defconfig b/configs/eb_cpu5282_internal_defconfig
index 52b29b2..2ce6ff9 100644
--- a/configs/eb_cpu5282_internal_defconfig
+++ b/configs/eb_cpu5282_internal_defconfig
@@ -8,6 +8,7 @@
 CONFIG_TARGET_EB_CPU5282=y
 CONFIG_MCFTMR=y
 CONFIG_SYS_BARGSIZE=1024
+CONFIG_SYS_MONITOR_LEN=131072
 CONFIG_SYS_MONITOR_BASE=0xF0000418
 CONFIG_BOOTDELAY=5
 CONFIG_BOOT_RETRY=y