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 <lokeshvutla@ti.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Roger Quadros <rogerq@ti.com>
Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index 0bf8274..fb5aa6f 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -44,6 +44,15 @@
 	help
 	  Enables support for the on-chip xHCI controller on Xilinx ZynqMP SoCs.
 
+config USB_XHCI_DRA7XX_INDEX
+	int "DRA7XX xHCI USB index"
+	range 0 1
+	default 0
+	depends on DRA7XX
+	help
+	  Select the DRA7XX xHCI USB index.
+	  Current supported values: 0, 1.
+
 endif # USB_XHCI_HCD
 
 config USB_EHCI_HCD