arc: move low-level interrupt and exception handlers in a separate file

This separation makes maintenance of code easier because those low-level
interrupt- or exception handling routines are pretty static and usually
require not much care while start-up code is a subject of modifications
and enhancements.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/arch/arc/lib/Makefile b/arch/arc/lib/Makefile
index ad66ac2..b1f1fbe 100644
--- a/arch/arc/lib/Makefile
+++ b/arch/arc/lib/Makefile
@@ -19,6 +19,7 @@
 obj-y += reset.o
 obj-y += timer.o
 obj-y += start.o
+obj-y += ints_low.o
 
 obj-$(CONFIG_CMD_BOOTM) += bootm.o