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/rcar3_salvator-x_defconfig b/configs/rcar3_salvator-x_defconfig
index 120b02c..4c1320d 100644
--- a/configs/rcar3_salvator-x_defconfig
+++ b/configs/rcar3_salvator-x_defconfig
@@ -13,6 +13,7 @@
 CONFIG_SYS_LOAD_ADDR=0x58000000
 CONFIG_FIT=y
 CONFIG_SUPPORT_RAW_INITRD=y
+CONFIG_SYS_MONITOR_BASE=0x00000000
 CONFIG_USE_BOOTARGS=y
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="tftp 0x48080000 Image; tftp 0x48000000 Image-r8a77950-salvator-x.dtb; booti 0x48080000 - 0x48000000"