drmmode: set plane zpos at init not when show cursor
drmmode: set plane zpos at init not when show cursor

The cursor plane 'zpos' property must be set to 1 to show the cursor.
However, this only needs to happen once, not every single time.

Now that we set this prop during init, we check for errors and fail
properly.

Signed-off-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

BUG=chromium:370411
TEST=move cursor, tap key to hide cursor, move cursor again. repeat on HDMI

Change-Id: If348b519c5ca1c4b77f77cc01ab929498daba8c9
Reviewed-on: https://chromium-review.googlesource.com/198389
Reviewed-by: Sean Paul <f9352ecf3e2294bdb914c99cca8d12601acec118@chromium.org>
Commit-Queue: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Tested-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

markyzq/armsoc-rockchip,markyzq/armsoc-rockchip