arc: Add support for native GDB

Signed-off-by: Anton Kolesov <anton.kolesov@synopsys.com>
arc: Remove temporary hack for Elf32_auxv_t

There were some issues with compiling gdbserver which caused commit 1c6fcf0
where we had to add contents of ARC-specific elf32.h file into the generic
gdbserver/linux-low.c file. This breaks build for native GDB. Apparently
changes to configure.tgt provided a better resolution for the original
issue or I don't know why behaviour changed for this issue.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
arc: Remove support for ABI v2 ptrace

Version of ARC Linux prior to 3.9 had a different ptrace ABI. gdbserver
supported it for some time as an option instead of new ABI. That is
redundant now, and only makes needlessly complex.

This patch removes old code.

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