mtd: msm_qpic_nand: Add support for performance stats

Add support to collect driver level performance statistics
on reads, writes and erases. Below are the commands to
enable, reset and read the stats -

echo 1 > /sys/module/msm_qpic_nand/parameters/enable_perfstats
echo > /sys/devices/platform/1b00000.nand/perf_stats
cat /sys/devices/platform/1b00000.nand/perf_stats

The module parameter "enable_perfstats" can also be enabled during
boot up by adding this to the kernel command line -
"msm_qpic_nand.enable_perfstats=1".

Change-Id: I20b35219a4bffd90682137969ecd5e854bea9a6b
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Pradeep P V K <ppvk@codeaurora.org>