Convert CONFIG_USB_XHCI_OMAP to Kconfig

This converts the following to Kconfig:
   CONFIG_USB_XHCI_OMAP

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am43xx_evm_defconfig b/configs/am43xx_evm_defconfig
index d7b12f2..b60090d 100644
--- a/configs/am43xx_evm_defconfig
+++ b/configs/am43xx_evm_defconfig
@@ -78,6 +78,7 @@
 CONFIG_SPL_DM_USB_GADGET=y
 CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_DWC3=y
+CONFIG_USB_XHCI_OMAP=y
 CONFIG_USB_DWC3=y
 CONFIG_USB_DWC3_OMAP=y
 CONFIG_USB_DWC3_GENERIC=y