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/cherryhill_defconfig b/configs/cherryhill_defconfig
index becb0a7..06987ab 100644
--- a/configs/cherryhill_defconfig
+++ b/configs/cherryhill_defconfig
@@ -12,6 +12,7 @@
 CONFIG_DEBUG_UART=y
 CONFIG_SMP=y
 CONFIG_GENERATE_MP_TABLE=y
+CONFIG_SYS_MONITOR_LEN=2097152
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="ext2load scsi 0:3 01000000 /boot/vmlinuz; zboot 01000000"