arch/arc: io.h - ad missing definitions

Without Linux data types "le32_to_cpu" and friends were not defined.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
configs/snps_haps51 - remove junk symbols from define

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
ARC: enable compilation without flash

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
ARC: initial support of ARC Xplorer board

Adds new configuration "snps_xplorer".
Debug UART is working.

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