feat(es8311): add digital input gain and restore 42dB HW max for ES3C28P/35P

- Add input-gain-percent property (0..2000, default 100) to everest,es8311 binding
- Extend Es8311Config with input_gain_percent, Es8311Data with input_gain float
- Implement get_input_gain_multiplier() so audio-stream can apply digital boost on top of HW gain
- Change HW gain mapping 100% -> 42dB (was 24dB) to restore +30dB behavior remembered from pre audio-stream driver (ES8311 supports 0/6/12/18/24/30/36/42 per vendor)
- Validate percent <=2000 in start_device()
- Set ES3C28P (2.8" color) and ES3C35P (3.5" color) DTS to input-gain-percent = <100> (no extra digital, pure HW 42dB max, software volume can lower)
- Fixes quiet mic even at 100% and allows tunable digital boost via devicetree for boards with quiet MEMS capsules

Devices/es3c28p/es3c28p.dts

@@ -91,6 +91,7 @@
 			compatible = "everest,es8311";
 			reg = <0x18>;
 			i2s = <&i2s0>;
+			input-gain-percent = <100>;
 		};
 	};
 

Devices/es3c35p/es3c35p.dts

@@ -88,6 +88,7 @@
 			compatible = "everest,es8311";
 			reg = <0x18>;
 			i2s = <&i2s0>;
+			input-gain-percent = <100>;
 		};
 	};