drm/tegra: Delete host1x_bo_ops->k(un)map

It doesn't have any callers anymore.

Aside: The ->mmap/munmap hooks have a bit a confusing name, they don't
do userspace mmaps, but a kernel vmap. I think most places use vmap
for this, except ttm, which uses kmap for vmap for added confusion.
mmap seems entirely for userspace mappings set up through mmap(2)
syscall.

Reviewed-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: linux-tegra@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20191118103536.17675-3-daniel.vetter@ffwll.ch