PC-98: Reflect 24khz/31khz selection in BIOS data area byte 0x54C and…

… remove redundant write to that byte

src/ints/bios.cpp

@@ -5045,6 +5045,8 @@ void gdc_16color_enable_update_vars(void) {
 	}
 }
 
+extern bool pc98_31khz_mode;
+
 class BIOS:public Module_base{
 private:
 	static Bitu cb_bios_post__func(void) {
@@ -5129,16 +5131,13 @@ class BIOS:public Module_base{
              * Ref: http://hackipedia.org/browse/Computer/Platform/PC,%20NEC%20PC-98/Collections/Undocumented%209801,%209821%20Volume%202%20(webtech.co.jp)/memsys.txt */
             mem_writeb(0x501,0x20 | memsize_real_code);
 
-            /* set up some default state */
-            mem_writeb(0x54C/*MEMB_PRXCRT*/,0x4F); /* default graphics layer off, 24KHz hsync */
-
             /* keyboard buffer */
             mem_writew(0x524/*tail*/,0x502);
             mem_writew(0x526/*tail*/,0x502);
 
             /* various BIOS flags */
             mem_writeb(0x53B,0x0F); // CRT_RASTER, 640x400 24.83KHz-hsync 56.42Hz-vsync
-            mem_writeb(0x54C,(enable_pc98_grcg ? 0x02 : 0x00) | (enable_pc98_16color ? 0x04 : 0x00)); // PRXCRT, 16-color G-VRAM, GRCG
+            mem_writeb(0x54C,(enable_pc98_grcg ? 0x02 : 0x00) | (enable_pc98_16color ? 0x04 : 0x00) | (pc98_31khz_mode ? 0x20/*31khz*/ : 0x00/*24khz*/)); // PRXCRT, 16-color G-VRAM, GRCG
             mem_writeb(0x54D,(enable_pc98_egc ? 0x40 : 0x00) | (gdc_5mhz_mode ? 0x20 : 0x00) | (gdc_5mhz_mode ? 0x04 : 0x00)); // EGC
             mem_writeb(0x597,(enable_pc98_egc ? 0x04 : 0x00/*FIXME*/)); // EGC
         }