gpu: host1x: Use DEFINE_SHOW_ATTRIBUTE to simplify debugfs code

Use DEFINE_SHOW_ATTRIBUTE helper macro to simplify the debugfs code for
the status and status_all entries. No functional change.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>