mips: Add MIPS64 support

mips: Add MIPS64 support

The patch adds support for processors implementing MIPS64 instruction set.

Change-Id: I79a983dfdead81553457a0f3e9e739a9785afaac
Signed-off-by: Konstantin Kostyukhin <kost@niisi.msk.ru>
Signed-off-by: Andrey Sidorov <anysidorov@gmail.com>
Signed-off-by: Aleksey Kuleshov <rndfax@yandex.ru>
Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
CC: Dongxue Zhang <elta.era@gmail.com>
CC: Paul Fertser <fercerpav@gmail.com>
CC: Salvador Arroyo <sarroyofdez@yahoo.es>
CC: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/2321
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>