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/kmcent2_defconfig b/configs/kmcent2_defconfig
index 0bade41..e534ca3 100644
--- a/configs/kmcent2_defconfig
+++ b/configs/kmcent2_defconfig
@@ -16,6 +16,7 @@
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
+CONFIG_SYS_MONITOR_BASE=0xEBF40000
 CONFIG_EVENT=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_EARLY_INIT_R=y