mapper-related updates and fixes (#491)

* m116: Fix support for Huang-2 chip

* Provide 8K CHR ram if no CHR rom/ram is provided due to bad headers

* m15: Implement CHR write-protect

* Update Namco 106

- Cleanup save state struct
- Implement nametable mirroring
- fix sound issue (fceux)

Co-authored-by: negativeExponent <negativeExponent@users.noreply.github.com>

src/boards/15.c

@@ -63,11 +63,19 @@ static void Sync(void) {
 	setprg8(0xC000, preg[2]);
 	setprg8(0xE000, preg[3]);
 	setmirror(((latched >> 6) & 1) ^ 1);
+	setchr8(0);
 }
 
 static DECLFW(M15Write) {
 	latchea = A;
 	latched = V;
+	/* cah4e3 02.10.19 once again, there may be either two similar mapper 15 exist. the one for 110in1 or 168in1 carts with complex multi game features.
+	   and another implified version for subor/waixing chinese originals and hacks with no different modes, working only in mode 0 and which does not
+	   expect there is any CHR write protection. protecting CHR writes only for mode 3 fixes the problem, all roms may be run on the same source again. */
+	if((latchea & 3) == 3)
+		SetupCartCHRMapping(0, CHRptr[0], 0x2000, 0);
+	else
+		SetupCartCHRMapping(0, CHRptr[0], 0x2000, 1);
 	Sync();
 }