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/eb_cpu5282_internal_defconfig b/configs/eb_cpu5282_internal_defconfig
index 2fa28a4..bb7854d 100644
--- a/configs/eb_cpu5282_internal_defconfig
+++ b/configs/eb_cpu5282_internal_defconfig
@@ -6,7 +6,7 @@
 CONFIG_TARGET_EB_CPU5282=y
 CONFIG_MCFTMR=y
 CONFIG_SYS_LOAD_ADDR=0x20000
-CONFIG_SYS_EXTRA_OPTIONS="SYS_MONITOR_BASE=0xF0000418"
+CONFIG_SYS_MONITOR_BASE=0xF0000418
 CONFIG_BOOTDELAY=5
 CONFIG_BOOT_RETRY=y
 CONFIG_BOOT_RETRY_TIME=-1