rpm-rail-stats: Add support to read RPM rail stats

Shared rails such as CX, MX are controlled by the RPM. RPM aggregates
the votes to these rails and sets the rails at a corner voltage to
satisfy the needs of all the masters.

Add support to read and print the CX, MX rail-stats from shared memory.

cat /d/rpm_rail_stats

Number of Rails:2
        rail:mx num_corners:4  current_corner:2  last_entered:1019693304
                corner:ret   time:0
                corner:svs   time:0
                corner:nom   time:1012700395189
                corner:turb  time:1015543861827
        rail:cx num_corners:5  current_corner:1  last_entered:1019698990
                corner:ret   time:0
                corner:svs2  time:8544797816954
                corner:svs   time:14534859650042
                corner:nom   time:8934117151715
                corner:turb  time:1015543586519

Change-Id: I730c4accc1bf4c152ef95f9ce9343a58022c2630
Signed-off-by: Karthik Parsha <kparsha@codeaurora.org>