BIOSF_VIDEOEN ($C00570): Enable/disable video layers
Only available on CD systems. All used registers are preserved.
The parameters are in bits 0~2 of D0:
|Def||Don't care||Enable video output|
(locks up ?)
|Enable sprites||Enable fix layer|
Enabling doesn't seem to work on real hardware ? (one way disable ?)
This function internaly uses the $FF0115, $FF0111 and $FF0119 memory mapped registers.