arm: usb: dra7xx: xHCI registers based on USB port index

arm: usb: dra7xx: xHCI registers based on USB port index

Modify the determination of the base address of xHCI registers of DRA7XX
targets.
Before the commit: by the target.
After the commit: by the USB port index.

Cc: Lokesh Vutla <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Roger Quadros <[email protected]>
Signed-off-by: Uri Mashiach <[email protected]>
Reviewed-by: Marek Vasut <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Reviewed-by: Roger Quadros <[email protected]>
Acked-by: Marek Vasut <[email protected]>
Acked-by: Marek Vasut <[email protected]>