nec/pc9801.cpp: provide some EGC defaults

Author: angelosa

hash/pc98.xml

@@ -20863,9 +20863,12 @@ Black screen [FDC] keeps reading chrn=(0, 0, 3, 256) in 2dd mode
 		<publisher>ビクターエンタテインメント (Victor Entertainment)</publisher>
 		<notes><![CDATA[
 Black screen, around PC=1fc76. Extensively uses 9821 [PEGC] MMIO.
+16 color mode has a column to the right shifted by one pixel on intro and gameplay
+Optional support for unsupported [graphic] and [sound] options
 ]]></notes>
 		<info name="alt_title" value="フラッシュバック" />
 		<info name="release" value="19940422" />
+		<info name="usage" value="Requires HDD DOS install" />
 		<part name="flop1" interface="floppy_5_25">
 			<feature name="part_id" value="Disk A"/>
 			<dataarea name="flop" size="1329680">

src/mame/nec/pc9801.cpp

@@ -1778,7 +1778,10 @@ MACHINE_START_MEMBER(pc9801vm_state,pc9801rs)
 	save_item(NAME(m_egc.start));
 	save_item(NAME(m_egc.mask));
 
-	save_item(NAME(m_grcg.mode));
+	save_item(STRUCT_MEMBER(m_grcg, mode));
+	//	save_pointer(STRUCT_MEMBER(m_grcg, tile), 4);
+	save_item(STRUCT_MEMBER(m_grcg, tile_index));
+
 	save_item(NAME(m_vram_bank));
 }
 
@@ -1860,6 +1863,12 @@ MACHINE_RESET_MEMBER(pc9801vm_state,pc9801rs)
 	}
 
 	m_dac1bit_disable = true;
+
+	// flashb in particular don't initialize the mask in 16 color mode
+	m_egc.regs[0] = 0xfff0;
+	m_egc.regs[1] = 0x00ff;
+	m_egc.mask = 0xffff;
+	m_egc.regs[7] = 0x000f;
 }
 
 MACHINE_RESET_MEMBER(pc9801bx_state,pc9801bx2)