staging: mt7621-dts: make use of new 'mt7621-clk'

staging: mt7621-dts: make use of new 'mt7621-clk'

Clocks for SoC mt7621 have been properly integrated so there is
no need to declare fixed clocks at all in the device tree. Remove
all of them, add new device tree nodes for mt7621-clk and update
the rest of the nodes to use them.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210410055059.13518-3-sergio.paracuellos@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>