house a screen tag and to find the screen at startup, providing an m_screen
object that can be used. One nice feature is that if there is only one
screen and no screen has been specified, it will auto configure to that
screen. This removes the need to explicitly specify a screen in the
configuration for a large chunk of drivers (though doing so never hurts).
A new macro MCFG_VIDEO_SET_SCREEN is provided, though devices are
encouraged to define their own that maps there so it is obvious which
device is being targeted. The device_video_interface's validation
function will error if an invalid screen is specified or if no screen
is provided but there are multiple screens present.
Updated all devices that currently had an m_screen in them to use the
device_video_interface instead. This also has the nice benefit of flagging
video-related devices for categorization purposes. It also means all
these devices inherit the same screen-finding behaviors. For devices
that had interfaces that specified a screen tag, those have been removed
and all existing structs updated.
Added an optional_device<screen_device> m_screen to the base driver_device.
If you name your screen "screen" (as most drivers do), you will have free
access to your screen this way.
Future updates include:
* Updating all devices referencing machine.primary_screen to use the
device_video_interface instead
* Updating all drivers referencing machine.primary_screen to use the
m_screen instead
* Removing machine.primary_screen entirely
