kern/54600: nouveau drm driver panics at boot with nvidia turing gpu

[code%boerschig.net@localhost]

>Number:         54600
>Category:       kern
>Synopsis:       nouveau drm driver panics at boot with nvidia turing gpu
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Oct 04 18:00:01 +0000 2019
>Originator:     MB
>Release:        NetBSD 9.0-BETA
>Organization:
>Environment:
NetBSD 9 amd64
>Description:
Booting NetBSD 9.0 daily build (201910020230Z) on AMD64 with a Geforce GTX 1650 (turing chipset), using either UEFI or MBR, gives kernel panic (transcript):

nouveau0: error: unknown chipset (167000a1)
uvm_fault(0xffffffff819852e0, 0x0, 1) -> e
(...)
db{0}> bt
nvkm_udevice_mthd() at netbsd:nvkm_udevice_mthd+0x188
nvkm_ioctl()       ... +0x21f
nvif_object_mthd() ... +0x92
nouveau_drm_load() ... +0xeb
drm_dev_register() ... +0xa5
drm_pci_attach()   ... +0x1a7
nouvea_pci_attach_real() ... +0xad
config_mountroot_thread  ... +0x70


Boot works with nouveau disabled in userconf. But then startx freezes.

>How-To-Repeat:
Just boot 9.0 BETA (2019/10/02) with a geforce gtx 1650.
I verified that current 9.99.15 behaves the same (similar backtrace).
>Fix: