gdb: Add OpenRISC or1k and or1knd target support

gdb: Add OpenRISC or1k and or1knd target support

This patch prepares the current GDB port of the OpenRISC processor from
https://github.com/openrisc/binutils-gdb for upstream merging.

Testing has been done with a cgen sim provided in a separate patch. This
has been tested with 2 toolchains. GCC [1] 5.4.0 from the OpenRISC
project with Newlib [2] and GCC 5.4.0 with Musl [3] 1.1.4.

It supports or1knd (no delay slot target).
The default target is or1k (with delay slot).

You can change the target arch with:

(gdb) set architecture or1knd
The target architecture is assumed to be or1knd

[1] https://github.com/openrisc/or1k-gcc
[2] https://github.com/openrisc/newlib
[3] https://github.com/openrisc/musl-cross

gdb/doc/ChangeLog:

2017-12-12  Stafford Horne  <shorne@gmail.com>
	    Stefan Wallentowitz  <stefan@wallentowitz.de>
	    Franck Jullien  <franck.jullien@gmail.com>
	    Jeremy Bennett  <jeremy.bennett@embecosm.com>

	* gdb.texinfo: Add OpenRISC documentation.

gdb/ChangeLog:

2017-12-12  Stafford Horne  <shorne@gmail.com>
	    Stefan Wallentowitz  <stefan@wallentowitz.de>
	    Stefan Kristiansson  <stefan.kristiansson@saunalahti.fi>
	    Franck Jullien  <franck.jullien@gmail.com>
	    Jeremy Bennett  <jeremy.bennett@embecosm.com>

	* configure.tgt: Add targets for or1k and or1knd.
	* or1k-tdep.c: New file.
	* or1k-tdep.h: New file.
	* features/Makefile: Add or1k.xml to build.
	* features/or1k.xml: New file.
	* features/or1k-core.xml: New file.
	* features/or1k.c: Generated.