drm/exynos: s3c6410_g3d: Zero correct register when detaching texture

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
drm/exynos: s3c6410_g3d: Add support for vertex textures

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
drm/exynos: s3c6410_g3d: Export vertex shader registers to userspace

This will eliminate the need to re-emit vertex shader every change of
attribute count and also enable remapping attributes.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>