bandai/wswan.cpp, bandai/wswan_v.cpp: Updates/Cleanups:

[cam900]

Common:

• Move palette related functions into bandai/wswan_v.cpp

bandai/wswan.cpp:

• Remove unused gfxdecode
• Make some variables constant
• Fix spacings

bandai/wswan_v.cpp:

• Add device_palette_interface for palette functions
• Split wonderswan color VDP device class into separated class
• Fix emulation incorrections
• Remove unused variables
• Reduce unnecessary function
• Reduce duplicates
• Fix typename for boolean flags
• Fix spacings
• Fix typo

reference: https://ws.nesdev.org/wiki/WSdev_Wiki

[cam900]

This PR after 87431d9:
mame wswan buffers -bench 90:
Average speed: 5290.27% (89 seconds)
Average speed: 5143.41% (89 seconds)
Average speed: 5171.78% (89 seconds)

mame wscolor buffers -bench 90:
Average speed: 5112.05% (89 seconds)
Average speed: 5188.16% (89 seconds)
Average speed: 5193.35% (89 seconds)

mame wscolor bluewing -bench 90:
Average speed: 2645.54% (89 seconds)
Average speed: 2700.49% (89 seconds)
Average speed: 2661.19% (89 seconds)

After some removal of virtual functions, then Performance reduction has been reduced.