mailbox: mtk-cmdq: Move and partially refactor clocks probe

Move the clocks probe to a new cmdq_get_clocks() function; while
at it, partially refactor the code:

Drop the clk_names[] array and assign clock names to the array
of clk_bulk_data with devm_kasprintf() instead, slightly reduce
the indentation for the multi-gce clock probe path and add a
comment describing the reason why we get clocks of other GCE
instance instead of just the clock from the one that it is
getting probed.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>