gdb/or1k: Add linux debugging support

gdb/or1k: Add linux debugging support

Up until now OpenRISC GDB only has supported bare metal debugging.  This
patch adds linux userspace debugging and core dump analysis support.

The changes are loosely based on nios2 and riscv implementations.

This was tested with linux 4.20 core dumps for executables linked
against musl libc.

bfd/ChangeLog:

	* elf32-or1k.c (or1k_grok_prstatus): New function.
	(or1k_grok_psinfo): Likewise.

gdb/ChangeLog:

	* Makefile.in (ALL_TARGET_OBS): Add or1k-linux-tdep.o.
	* configure.tgt: Add or1k*-*-linux*.
	* or1k-linux-tdep.c: New file.
	* or1k-tdep.c (or1k_gdbarch_init): Call gdbarch_init_osabi.