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/10m50_defconfig b/configs/10m50_defconfig
index 517c3b0..5a4290a 100644
--- a/configs/10m50_defconfig
+++ b/configs/10m50_defconfig
@@ -8,6 +8,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="10m50_devboard"
 CONFIG_SYS_LOAD_ADDR=0xcc000000
 CONFIG_FIT=y
+CONFIG_SYS_MONITOR_BASE=0xCFF80000
 # CONFIG_AUTOBOOT is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y