Add pstore support for the nexus7. This was useful in debugging
a crash where the cpus were getting stuck with irqs off and
serial output wasn't reliably working.

Cc: Kees Cook <keescook@chromium.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Andy Gross <andy.gross@linaro.org>
Cc: Vinay Simha <vinaysimha@inforcecomputing.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>