MCT optimization for SBA at 256 kbps (113)

The following initial changes are in main under switch FIX_I1_113 switch:

• Make sure the sum of calculated channel ratios is BITRATE_MCT_RATIO_RANGE.

• Avoid hardcoding of bit ratios and use the bit distribution given by ivas_spar_bitrate_dist().

Switch is currently deactivated and further review/verification is pending.

Additional ideas that could be implemented and tested:

• Bits saving by not coding all channel bit ratios at 256 kbps.

• Avoid hardcoding of bit ratios if a channel pair is selected (high correlation scenario).