Revision of the number of channel buffers in OMASA

When decoding the OMASA bitstream, the number of channel buffers seems to be unnecessarily high and can be reduced. Consequently, the decoder RAM would be reduced.

This concerns buffers

• st_ivas->p_output_f[][] which is allocated using function ivas_get_nchan_buffers_dec()
• st_ivas->hTcBuffer->tc_buffer[] which is allocated based on parameter st_ivas->hTcBuffer->nchan_buffer_full

Note: this issue was discovered when debugging #1220 (closed). In order to clearly separate the decoder crash from #1120 (closed) and the memory optimization, there are two separate MRs !1858 (merged) and !1860 (merged). Alternatively, both fixes can be merged into one MR. Personally, I have no preference for the way forward.