msm: vidc: Enhance the STOP command for encoder

Currently, STOP command is valid only for decoder. Enhance it
for encoder sessions, so that clients can avoid zero_bytes_used
error for encoders as well.

CRs-Fixed: 2078801
Change-Id: I25148e07ba883a771177864581942fcba0a2b24c
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>