V4L2Decoder: increase the number of output buffers to prevent ccodec timeout

CCodecBufferChannel (CCBC) set the number of output slots to
"output delay + kSmoothnessFactor". CCBC would pause sending input
buffers to the component when all the output slots are filled by
pending decoded buffers.  If the available output buffers are exhausted
at the output slots before CCBC pause sending input buffers, CCodec
would treat this situation as timeout easily. This CL increases the
number of output buffer more than the number of output slots to
prevent this situation from happening.

Note: CCodec measures the elapsed time between CCBC passes a input
buffer to the component and the component returns the corresponding
output buffer back to CCBC. If the elapsed time is greater than a
threshold, then CCodec considers the component stop working.

Bug: 184020290
Test: android.media.cts.VideoEncoderTest#testGoogH264Flex1080p

Change-Id: I38502d77d247499f1fcc5b434f18ad5e6edbfcb9
(cherry picked from commit 5d06eade6f296b88eacb8619e04ba96a9e60deb7)