Fix 3 band equalizer in Genesis (#2008)

If you tried setting your gains to 100 in the previous patch, it worked sort of, but I decided to incorporate ekeeke/Genesis-Plus-GX@f6f4556 as well to actually fix it completely, and rescale the setting properly so that 1.0 really is neutral gain.

Fixes #1319

src/BizHawk.Emulation.Cores/Consoles/Sega/gpgx64/GPGX.ISettable.cs

@@ -265,18 +265,18 @@ namespace BizHawk.Emulation.Cores.Consoles.Sega.gpgx
 
 			[DisplayName("Three band low gain")]
 			[Description("Only active when filter type is three band")]
-			[DefaultValue((short)1)]
-			public short LowGain { get; set; }
+			[DefaultValue(1f)]
+			public float LowGain { get; set; }
 
 			[DisplayName("Three band mid gain")]
 			[Description("Only active when filter type is three band")]
-			[DefaultValue((short)1)]
-			public short MidGain { get; set; }
+			[DefaultValue(1f)]
+			public float MidGain { get; set; }
 
 			[DisplayName("Three band high gain")]
 			[Description("Only active when filter type is three band")]
-			[DefaultValue((short)1)]
-			public short HighGain { get; set; }
+			[DefaultValue(1f)]
+			public float HighGain { get; set; }
 
 			[Description("Magic pink by default. Requires core reboot")]
 			[TypeConverter(typeof(UintToHexConverter))]
@@ -291,9 +291,9 @@ namespace BizHawk.Emulation.Cores.Consoles.Sega.gpgx
 					LowPassRange = LowPassRange,
 					LowFreq = LowFreq,
 					HighFreq = HighFreq,
-					LowGain = LowGain,
-					MidGain = MidGain,
-					HighGain = HighGain,
+					LowGain = (short)(LowGain * 100),
+					MidGain = (short)(MidGain * 100),
+					HighGain = (short)(HighGain * 100),
 					BackdropColor = BackdropColor
 				};
 			}

waterbox/gpgx/cinterface/cinterface.c

@@ -546,9 +546,9 @@ GPGX_EX int gpgx_init(
 	config.lp_range = settings->LowPassRange; //0x9999; /* 0.6 in 16.16 fixed point */
 	config.low_freq = settings->LowFreq; //880;
 	config.high_freq = settings->HighFreq; //5000;
-	config.lg = settings->LowGain; //1.0;
-	config.mg = settings->MidGain; //1.0;
-	config.hg = settings->HighGain; //1.0;
+	config.lg = settings->LowGain; //100;
+	config.mg = settings->MidGain; //100;
+	config.hg = settings->HighGain; //100;
 	config.dac_bits = 14; /* MAX DEPTH */
 	config.ym2413= 2; /* AUTO */
 	config.mono  = 0; /* STEREO output */