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/xtfpga_defconfig b/configs/xtfpga_defconfig
index 0e1a193..ff3f260 100644
--- a/configs/xtfpga_defconfig
+++ b/configs/xtfpga_defconfig
@@ -5,6 +5,7 @@
 CONFIG_ENV_SECT_SIZE=0x20000
 CONFIG_XTFPGA_KC705=y
 CONFIG_SYS_LOAD_ADDR=0x02000000
+CONFIG_SYS_MONITOR_BASE=0xF6000000
 CONFIG_DYNAMIC_SYS_CLK_FREQ=y
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_BOOTDELAY=10