drm/msm/gem: Separate object and vma unpin

Previously the BO_PINNED state in the submit was tracking two related
but different things: (1) that the buffer object was pinned, and (2)
that the vma (mapping within a set of pagetables) was pinned.  But with
fenced vma unpin (needed so that userspace couldn't race with retire
path for releasing a vma) these two were decoupled.  The fact that the
BO_PINNED flag was already cleared meant that we leaked the bo pin count
which should have been dropped when the submit was retired.

So split this state into BO_OBJ_PINNED and BO_VMA_PINNED, so they can be
dropped independently.

Fixes: 95d1deb0 ("drm/msm/gem: Add fenced vma unpin")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/487559/
Link: https://lore.kernel.org/r/20220527172341.2151005-1-robdclark@gmail.com