arc: Remove extra commands

Use generic OpenOCD commands where possible.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
arc: Remove arc_trgt.{c,h} files

It contained a single functions which was printing "not implemented".

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
arc: Remove arc_core.{c,h} files

Files contained two functions: one "feature not implemented yet", another
which has been called from a single place. Removed first one, integrated
second one to the place where it is called.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
arc: Remove arc.{c,h} files

There were two small to justify existence, especially since we have only
one target "arc32". Content integrated into arc32.{c,h} files.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>