Revert "pvr: Make pvr_cmd_pack() macro clearly internal"

Revert "pvr: Make pvr_cmd_pack() macro clearly internal"

This reverts commit 27c57b86500ce48154533d78b74350c31152b2f3.

The driver doesn't always pack or emit words directly. In some
cases it might be desirable to store the struct equivalent for the
control word and emit/pack at a later stage. Thus reverting to
expose pvr_cmd_pack().
One such use case is in the following commit.

Signed-off-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Rajnesh Kanwal <rajnesh.kanwal@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18124>