Convert CONFIG_SYS_MONITOR_BASE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MONITOR_BASE

Note that for how this is re-used on some PowePC platforms, we introduce
CONFIG_SPL_SYS_MONITOR_BASE and CONFIG_TPL_SYS_MONITOR_BASE and use the
CONFIG_VAL macro to get the correct value at build time, in the code.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/adp-ae3xx_defconfig b/configs/adp-ae3xx_defconfig
index 9f7b268..c353b84 100644
--- a/configs/adp-ae3xx_defconfig
+++ b/configs/adp-ae3xx_defconfig
@@ -11,6 +11,7 @@
 CONFIG_TARGET_ADP_AE3XX=y
 CONFIG_SYS_LOAD_ADDR=0x300000
 CONFIG_FIT=y
+CONFIG_SYS_MONITOR_BASE=0x88000000
 CONFIG_BOOTDELAY=3
 # CONFIG_AUTO_COMPLETE is not set
 CONFIG_SYS_PROMPT="NDS32 # "