KMS seems broken in vc4.ko

[Ryutaroh Matsumoto]

> I'm still confused, did you blacklist vc4 or v3d? 

For the emails sent to you and linux-rpi-kernel on MARCH 12 and LATER,
I blacklisted v3d and loaded vc4.

In https://github.com/raspberrypi/linux/issues/4202
I loaded both v3d and vc4.

Are these clear enough???

> I mean, it depends on what mesa and kmscube are trying to do? Can you
> enable drm.debug and see if there's any clearer error message?

I have no access to my RPi4B now. I will report it back when I return from my travel.

Best regards, Ryutaroh