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/amcore_defconfig b/configs/amcore_defconfig
index d64fb84..b104795 100644
--- a/configs/amcore_defconfig
+++ b/configs/amcore_defconfig
@@ -8,6 +8,7 @@
 CONFIG_TARGET_AMCORE=y
 CONFIG_MCFTMR=y
 CONFIG_SYS_LOAD_ADDR=0x20000
+CONFIG_SYS_MONITOR_BASE=0xFFC00400
 CONFIG_BOOTDELAY=1
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="bootm ffc20000"