add more mosys platform information to chrome://system

To be able to debug various hardware related issues on Spring, we need
to know precisely the board revision inside the machine.
"mosys platform version" is returning a decoded form of the board
revision id and various other "mosys platform" subcommands give
hw specific info.
Let's add these to chrome://system and feedback reports.

BUG=chrome-os-partner:21674
TEST=on Spring, open chrome://system and see the board revision properly
reported under "platform_info", fill a feedback and also see it in the
feedback "Product Specific Data"

Original-Change-Id: I8e164ed0aebdfa8aaef3e6a01b4e2567775a0a64
Reviewed-on: https://gerrit.chromium.org/gerrit/64708
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit b6225c2b38a2b8cb13388cb9584225a2bcc3f8c9)

Change-Id: I44b28dce1638f836004387154b3ee30ccb2f69bb
Reviewed-on: https://gerrit.chromium.org/gerrit/65589
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>