HACK: UPSTREAM: add pstore console support

HACK: UPSTREAM: add pstore console support

Pstore console keeps a console in ram that is available next boot via:

/dev/pstore/console-ramoops

PSTORE_CONSOLE is upstream but there has been a lot of churn in the
pstore code that preceded PSTORE_CONSOLE. So rather than backport
a dozen or so patches, I've added support from scratch and made the
user-space interface consistent with what is upstream.

BUG=chromium-os:33273
TEST=See below.

$ reboot
$ cat /dev/pstore/console-ramoops
$ echo bug > /proc/breakme

Crash

$ cat /dev/pstore/console-ramoops
$ cat /dev/pstore/dmesg-ramoops-0

EC reset

$ cat /dev/pstore/console-ramoops
$ rm /dev/pstore/dmesg-ramoops-0
$ reboot
$ cat /dev/pstore/console-ramoops
$ cat /dev/pstore/dmesg-ramoops-0
$ echo panic > /proc/breakme

Crash

$ cat /dev/pstore/console-ramoops
$ cat /dev/pstore/dmesg-ramoops-0

Change-Id: I1069d974679577c980276f822f7835f9d221d12b
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/29960
Reviewed-by: Kees Cook <keescook@chromium.org>