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-be_defconfig b/configs/arcangel4-be_defconfig
index 5d2e126..979f26e 100644
--- a/configs/arcangel4-be_defconfig
+++ b/configs/arcangel4-be_defconfig
@@ -2,3 +2,4 @@
 CONFIG_TARGET_ARCANGEL4=y
 CONFIG_SYS_CLK_FREQ=70000000
 CONFIG_CPU_BIG_ENDIAN=y
+CONFIG_SYS_TEXT_BASE=0x81000000