cache_erp: Use seq_printf and modernize procfs code

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: Ifc11287a8aefa8b2af3fb7d68fd96c1db8f2f098
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>