usb: cdns3: Use dma_pool_* api to alloc trb pool

Allocation of DMA coherent memory in atomic context using
dma_alloc_coherent() might fail on platforms with smaller
DMA region.

To fix it, dma_alloc_coherent() is replaced with dma_pool
API to allocate a smaller chunk of DMA coherent memory for
TRB rings.

Fixes: 7733f6c3

 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Sanket Parmar <sparmar@cadence.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>