msm: vidc: amend buffer counts calculation

- Consider thumbnail mode while calculating buffer counts
- decide batching in reconfiguration event so that driver
  returns proper min buffer count when client query for it

Change-Id: I4d5373e78d43592caf0cef59f2f8801d20014efd
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>