xserver-xorg-core includes modesetting_drv.so, move to xserver-xorg-video-kms

[Vito Caputo <vcaputo@pengaru.com>]

Hello list,

I am not subscribed so please reply to me directly.

Today I went down a bit of a wild goose chase caused in part by
confusion established by the debian packaging of XOrg.

The modesetting_drv.so driver is a video driver, and should be packaged
separately as such in something like xserver-xorg-video-kms fulfilling
xorg-driver-video.

As-is, even if I'm using the modesetting driver, my system wants
xorg-driver-video fulfilled and insists on having something like
xserver-xorg-video-intel installed.

Though I can safely remove /usr/lib/xorg/modules/drivers/intel_drv.so and have
my Xorg continue to function normally, when I attempt to remove
xserver-xorg-video-intel I am faced with this:

```
# apt-get remove --purge xserver-xorg-video-intel
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  libxatracker2 xserver-xorg-video-all xserver-xorg-video-amdgpu
  xserver-xorg-video-ati xserver-xorg-video-fbdev xserver-xorg-video-nouveau
  xserver-xorg-video-qxl xserver-xorg-video-radeon xserver-xorg-video-vesa
  xserver-xorg-video-vmware
Suggested packages:
  firmware-amd-graphics xserver-xorg-video-r128 xserver-xorg-video-mach64
Recommended packages:
  xserver-xorg-video-intel
The following packages will be REMOVED:
  xserver-xorg-video-intel*
The following NEW packages will be installed:
  libxatracker2 xserver-xorg-video-all xserver-xorg-video-amdgpu
  xserver-xorg-video-ati xserver-xorg-video-fbdev xserver-xorg-video-nouveau
  xserver-xorg-video-qxl xserver-xorg-video-radeon xserver-xorg-video-vesa
  xserver-xorg-video-vmware
0 upgraded, 10 newly installed, 1 to remove and 12 not upgraded.
Need to get 2,630 kB of archives.
After this operation, 2,658 kB of additional disk space will be used.
Do you want to continue? [Y/n] 
```

Thanks,
Vito Caputo