Fix EGA port 3C2h readback of switches for machine=ega200 [#5036]

CHANGELOG

@@ -1,6 +1,8 @@
 Next:
+  - Correct EGA switch readback from port 3C2h to reflect a value of 0x8
+    instead of 0x9 when machine=ega200 (joncampbell123).
   - Correct BIOS data area value that holds the "EGA switches" to reflect
-    200-line EGA "emulation" when machine=ega200. Value 0x08 instead of 0x09.
+    200-line EGA "emulation" when machine=ega200. Value 0x08 instead of 0x09
     (joncampbell123).
   - Correct mode parameters for CGA 640x200 2-color mode when using
     machine=ega200 so that it displays correctly. (joncampbell123)

src/hardware/vga_misc.cpp

@@ -159,6 +159,8 @@ static Bitu read_p3c8(Bitu port,Bitu iolen) {
 	return 0x10;
 }
 
+extern bool ega200;
+
 static Bitu read_p3c2(Bitu port,Bitu iolen) {
     (void)port;//UNUSED
     (void)iolen;//UNUSED
@@ -168,14 +170,9 @@ static Bitu read_p3c2(Bitu port,Bitu iolen) {
 	else if (IS_VGA_ARCH) retval = 0x60;
 
 	if(IS_EGAVGA_ARCH) {
-		switch((vga.misc_output>>2)&3) {
-			case 0:
-			case 3:
-				retval |= 0x10; // 0110 switch positions
-				break;
-			default:
-				break;
-		}
+		uint8_t setting = ~((!IS_VGA_ARCH && ega200)?0x08:0x09)/*bits are inverted*/;
+		const uint8_t bit = (vga.misc_output>>2)&3;
+		if (setting & (1 << bit)) retval |= 0x10;
 	}
 
 	if (vga.draw.vret_triggered) retval |= 0x80;