drm/via: Rename via_drv to via_dri1

The via driver implements the DRI1 interface, and we have a new
implementation of the via driver coming that supports atomic
modesetting.

It is not acceptable just to replace the existing driver so
this is first step to make it a single-file implementation allowing
it to stay without interfering with the new driver.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Kevin Brace <kevinbrace@bracecomputerlab.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220713170202.1798216-2-sam@ravnborg.org