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/socrates_defconfig b/configs/socrates_defconfig
index 1eb72d3..96d0691 100644
--- a/configs/socrates_defconfig
+++ b/configs/socrates_defconfig
@@ -10,6 +10,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
+CONFIG_SYS_MONITOR_BASE=0xFFF80000
 CONFIG_BOOTDELAY=1
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="run boot_nor"