drm/via: Embed via_dmablit in via_dri1

Embed some of the header file in via_drv.h and
the rest in via_dri1.c
While embedding deleted extra empty lines and functions that
has no external users are made static.

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/20220713170202.1798216-8-sam@ravnborg.org