dma: ti: k3-udma: Switch to k3_ringacc_request_rings_pair

We only request ring pairs via K3 DMA driver, switch to use the new
k3_ringacc_request_rings_pair() to simplify the code.

As a good side effect, all boot stages now use exposed RING mode which
avoid maintaining proxy mode for 32 bit R5 core.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>