drm/via: Embed via_drv.h in via_dri1

With this change the driver is now a signle file driver.
The only remaning heder file describes the HW and can be shared with the
new openchrome 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/20220713170202.1798216-10-sam@ravnborg.org