riscv: dts: thead: update TH1520 dma and timer nodes to use clock controller

riscv: dts: thead: update TH1520 dma and timer nodes to use clock controller

Change the dma-controller and timer nodes to use the APB clock provided
by the AP_SUBSYS clock controller.

Remove apb_clk reference from BeagleV Ahead and LPI4a dts.

Link: https://git.beagleboard.org/beaglev-ahead/beaglev-ahead/-/tree/main/docs
Signed-off-by: Drew Fustini <dfustini@tenstorrent.com>