Audio: Multiband DRC: Use optimized 4th order IIR filter version

[singalsu]

The simpler 4th order hard-coded IIR version saves MCPS in in band split filter bank and emphasis/de-emphasis IIR filters.

[singalsu]

WIP - I'll see if I can further improve the HiFi4 and HiFi5 IIR versions.

[singalsu]

WIP - I'll see if I can further improve the HiFi4 and HiFi5 IIR versions.

Just for the record, I tried this change for the inner loop but it's in practical application a bit slower (1.35 MCPS, while a separate test code indicated 296 cycles vs. earlier 310 cycles) than this proposed version:

		/* Load data */
		AE_LA32X2X2_IP(delay_y2y1, delay_x2x1, data_r_align, delay_r);

		/* Load coefficients */
		AE_LA32X2X2_IP(coef_a2a1, coef_b2b1, coef_align, coefp);
		AE_LA32X2X2_IP(coef_b0shift, gain, coef_align, coefp);

		acc = AE_MULF32RA_HH(AE_MOVAD32_H(coef_b0shift), in);  /* acc = b0 * in */
		AE_MULAAFD32RA_HH_LL(acc, coef_a2a1, delay_y2y1); /* + a2 * y2 + a1 * y1 */
		AE_MULAAFD32RA_HH_LL(acc, coef_b2b1, delay_x2x1); /* + b2 * x2 + b1 * x1 */
		AE_PKSR32(delay_y2y1, acc, 1);		     /* y2 = y1, y1 = acc(q1.31) */
		delay_x2x1 = AE_SEL32_LL(delay_x2x1, in);   /* x2 = x1, x1 = in */

		/* Store data */
		AE_SA32X2X2_IP(delay_y2y1, delay_x2x1, data_w_align, delay_w);

		/* Apply gain */
		acc = AE_MULF32R_LL(AE_MOVAD32_H(gain), delay_y2y1);	/* acc = gain * y1 */
		acc = AE_SLAI64S(acc, 17);		/* Convert to Q17.47 */

		/* Apply biquad output shift right parameter and then
		 * round and saturate to 32 bits Q1.31.
		 */
		acc = AE_SRAA64(acc, AE_MOVAD32_L(coef_b0shift));
		in = AE_ROUND32F48SSYM(acc);

So the current version with 7 words coefficients set becomes the proposal. Padding it to 8 words for two 128 bits loads didn't improve. In addition it needed a separate new function to copy and align the existing format coefficients.