Add emulation of IBM PS/1 Model 2121.

As part of this :
- FDC Specify command now completes immediately
- Implemented keyboard system flag status
- Added ability to remap 384kb reserved memory to above extended memory

src/Makefile.am

@@ -29,7 +29,7 @@ sound_speaker.c sound_ssi2001.c sound_wss.c sound_ym7128.c soundopenal.c tandy_e
 timer.c um8669f.c um8881f.c vid_ati_eeprom.c vid_ati_mach64.c vid_ati18800.c vid_ati28800.c \
 vid_ati68860_ramdac.c vid_cga.c vid_cl5429.c vid_ega.c vid_et4000.c vid_et4000w32.c vid_hercules.c \
 vid_icd2061.c vid_ics2595.c vid_incolor.c vid_mda.c vid_olivetti_m24.c vid_oti067.c vid_paradise.c vid_pc200.c \
-vid_pc1512.c vid_pc1640.c vid_pcjr.c vid_s3.c vid_s3_virge.c vid_sdac_ramdac.c \
+vid_pc1512.c vid_pc1640.c vid_pcjr.c vid_ps1_svga.c vid_s3.c vid_s3_virge.c vid_sdac_ramdac.c \
 vid_stg_ramdac.c vid_svga.c vid_svga_render.c vid_tandy.c vid_tandysl.c vid_tgui9440.c \
 vid_tkd8001_ramdac.c vid_tvga.c vid_unk_ramdac.c vid_vga.c vid_voodoo.c video.c wd76c10.c \
 x86seg.c x87.c xtide.c sound_dbopl.cc sound_resid.cc dosbox/dbopl.cpp \