f_gsi: Increase MBIM IN aggregation to 31KB

This change increases MBIM IN aggregation and related TRB buffer size
from 16KB to 31KB. With this aggregation change, DL throughput is
increased form 4.2 Gbps to 4.7 Gbps. Also reduced OUT buffer size from
31KB to 16 KB (i.e. as equal to size of OUT aggregation).

Change-Id: Ida6444536f27f385034fefc71e663d7b7ce5626f
Signed-off-by: Mayank Rana <mrana@codeaurora.org>