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

Drivers/es8311-module/include/drivers/es8311.h

@@ -25,6 +25,14 @@ struct Es8311Config {
     uint8_t address;
     /** I2S controller device that carries audio data */
     struct Device* i2s_device;
+    /**
+     * Extra fixed digital gain multiplier applied by audio_stream on top of the ES8311's
+     * own hardware ADC gain (0..24dB), as an integer percentage (100 = 1.0x / no extra boost).
+     * Small MEMS mic capsules can still sound quiet even near max hardware gain; this is for
+     * boards where 24dB hardware gain alone isn't enough. devicetree has no float property type,
+     * hence the x100 integer encoding.
+     */
+    uint16_t input_gain_percent;
 };
 
 #ifdef __cplusplus