arc: move SYS_MONITOR_BASE setup in Konfig

Following SPARK ARC now has SYS_MONITOR_BASE setup via Kconfig.
This makes "include/configs/*.h" cleaner and more flexible.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/configs/arcangel4_defconfig b/configs/arcangel4_defconfig
index a63ef21..797595f 100644
--- a/configs/arcangel4_defconfig
+++ b/configs/arcangel4_defconfig
@@ -1,3 +1,4 @@
 CONFIG_ARC=y
 CONFIG_TARGET_ARCANGEL4=y
 CONFIG_SYS_CLK_FREQ=70000000
+CONFIG_SYS_TEXT_BASE=0x81000000