msm: pm-stats: Move to seq_file and friends

In future kernels create_proc_entry() is going to be removed.
Let's modernize this code and use regular file operations and
seq_printf() to avoid experiencing compilation problems in future
kernels.

Change-Id: Ibeca64a8346d33e1b66b089990c17f1b1dbaf5db
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Anji Jonnala <anjir@codeaurora.org>