clk: mediatek: mt7986: rename CB_CKSQ_40M to TOP_XTAL

Upstream kernel linux clock include use TOP_XTAL instead of CB_CKSQ_40M.
Rename this clock to the upstream kernel in preparation for support of
OF_UPSTREAM.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
3 files changed