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/MCR3000_defconfig b/configs/MCR3000_defconfig
index f174865..1c74e4a 100644
--- a/configs/MCR3000_defconfig
+++ b/configs/MCR3000_defconfig
@@ -18,6 +18,7 @@
 CONFIG_SYS_DER=0x2002000F
 CONFIG_SYS_LOAD_ADDR=0x200000
 CONFIG_OF_BOARD_SETUP=y
+CONFIG_SYS_MONITOR_BASE=0x04000000
 CONFIG_BOOTDELAY=5
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="\nEnter password - autoboot in %d sec...\n"