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/r2dplus_defconfig b/configs/r2dplus_defconfig
index 8b5c8ff..f12c09a 100644
--- a/configs/r2dplus_defconfig
+++ b/configs/r2dplus_defconfig
@@ -7,6 +7,7 @@
 CONFIG_SYS_CLK_FREQ=60000000
 CONFIG_TARGET_R2DPLUS=y
 CONFIG_SYS_LOAD_ADDR=0x8e000000
+CONFIG_SYS_MONITOR_BASE=0xA0000000
 CONFIG_BOOTDELAY=-1
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttySC0,115200"