pixel_stats: add access to PSI information

Add access to PSI information, i.e. /proc/pressure/xyz,
where xyz=cpu, io, or memory.

Test: local test
Bug: 233841658
Merged-In: Ic433cd2ebfdd24694ed63bee118e30e286c11b41
(cherry picked from commit 69d59aa6e7b3e9897ffc811558708d322d4bed2a)
Signed-off-by: Robin Hsu <robinhsu@google.com>
Change-Id: I0e45ec31bbf470504efdd0143bbecef31bce299e
1 file changed