arc: move common sources in library

"reset.c" and "cpu.c" have no architecture-specific code at all.
Others are applicable to either ARC CPU.

This change is a preparation to submission of ARCv2 architecture port.

Even though ARCv1 and ARCv2 ISAs are not binary compatible most of
built-in modules still have the same programming model - AUX registers
are mapped in the same addresses and hold the same data (new featues
extend existing ones).

So only low-level assembly code (start-up, interrupt handlers) is left
as CPU(actually ISA)-specific. This significantyl simplifies maintenance
of multiple CPUs/ISAs.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Igor Guryanov <guryanov@synopsys.com>

arch/arc/cpu/arc700/Makefile

@@ -4,9 +4,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y	+= cache.o
-obj-y	+= cpu.o
-obj-y	+= interrupts.o
-obj-y	+= reset.o
-obj-y	+= start.o
-obj-y	+= timer.o
+obj-y += start.o

arch/arc/lib/Makefile

@@ -4,6 +4,9 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+obj-y += cache.o
+obj-y += cpu.o
+obj-y += interrupts.o
 obj-y += sections.o
 obj-y += relocate.o
 obj-y += strchr-700.o
@@ -13,4 +16,7 @@ obj-y += strlen.o
 obj-y += memcmp.o
 obj-y += memcpy-700.o
 obj-y += memset.o
+obj-y += reset.o
+obj-y += timer.o
+
 obj-$(CONFIG_CMD_BOOTM) += bootm.o