convert "bnstars1" to use dual palettes.

note, needed to add PALETTE_FORMAT_XBRG for this game, also READ16_MEMBER(palette_device::read) IS necessary here because the ram is installed on every other word
AM_DEVREADWRITE16("palette",  palette_device, read, write, 0x0000ffff) AM_SHARE("palette")
and without the 'read' handler the wrong data gets read back for the RAM checks.