mtd: Collect bad block count for ecc stats lazily

Normally bad block counts for ECC stats are collected
during boot time. This can be done lazily when the
ECCGETSTATS ioctl is invoked on the partition.

This can significantly decrease boot time, depending
on the size of the partition. Also rescanning on every
ioctl invocation helps in having the latest bad block count
rather than depending on the count that is collected during boot.

Change-Id: I43d7a769a1d4ef769823d0b5bbe132adb474f892
Signed-off-by: Murali Palnati <palnatim@codeaurora.org>
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>
Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>
Signed-off-by: Pradeep P V K <ppvk@codeaurora.org>
Signed-off-by: Sarthak Garg <sartgarg@codeaurora.org>