BIOSF VIDEOEN

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:

Bit	7	6	5	4	3	2	1	0
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.