This commit adds basic architectural support for the OpenRISK mor1kx...

This commit adds basic architectural support for the OpenRISK mor1kx architecture.  The initial commit was verified on a Qemu simulation but is otherwise untested.

Squashed commit of the following:

Author: Gregory Nutt <gnutt@nuttx.org>
    Update README.
    configs/or1k:  Should include header file file where exported functin is prototyped.
    arch/or1k/src:  Eliminate some warnings.
    arch/or1k:  Complete review
    Fix some recently introduced build issues
    configs/or1k/nsh:  Convert to proper, compressed defconfig file.
    Another README update.
    Update README
    configs/or1k:  Updates from initial review.
    Update README.

Author: Matt Thompson <matt@extent3d.com>

    or1k: Added configurable CPU frequency to Kconfig. Calculate tick timer match period based on configured frequency.
    OpenRISC: Enable instruction and data cache
    OpenRISC: Initial support.