arc: replace copyright header with SPDX

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: add guard wrapper to header file

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: empty header

This one is required only to make compiler happy for drivers that
mention <asm/hardware.h>

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: remove copyright notice since there's nothing from us was added

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: cosmetics in headers

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: remove extra newline

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: remove extra temporary variable

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
xplorer: update comment on D$ usage

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
arc: fix compile-time warnings

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