ARCv2: cleanups in defconfig/DT

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARC: fix /proc/cpuinfo for offline cpus

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARCv2: use prefetch mnemonic

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARCv2: use PREFETCHW - there's room for more for later

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARC: rename default defconfig

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARCv2: rename default defconfig

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>