psi: Improve ftrace events

Improve readability of logs by converting hex values to decimal,
and printing memstall deltas instead of absolute values.

Change-Id: I43f21dd9817b540184ce05fd7151459d3502ea28
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>