emu/sound.cpp: Made -volume in source file INI or higher priority
context take precedence over volume read from CFG file. This matches
behaviour of -bgfx_screen_chains.
emu/input.cpp: Made explicit -no{mouse|joystick|lightgun} take
precedence over -{mouse|trackball|adstick|paddle}_device etc. from lower
priority levels.
Alos got rid of a bunch of unnecessary simple_list.