drm/vmwgfx: Add new keep_resv BO param

Adds a new BO param that keeps the reservation locked after creation.
This removes the need to re-reserve the BO after creation which is a
waste of cycles.

This also fixes a bug in vmw_prime_import_sg_table where the imported
reservation is unlocked twice.

Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Fixes: b32233ac ("drm/vmwgfx: Fix prime import/export")
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250110185335.15301-1-ian.forbes@broadcom.com