Convert CONFIG_OMAP_USB_PHY to Kconfig

This converts the following to Kconfig:
   CONFIG_OMAP_USB_PHY

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/am43xx_hs_evm_defconfig b/configs/am43xx_hs_evm_defconfig
index bed0583..e8a641e 100644
--- a/configs/am43xx_hs_evm_defconfig
+++ b/configs/am43xx_hs_evm_defconfig
@@ -60,6 +60,7 @@
 CONFIG_USB_DWC3_GADGET=y
 CONFIG_USB_DWC3_OMAP=y
 CONFIG_USB_DWC3_PHY_OMAP=y
+CONFIG_OMAP_USB_PHY=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_MANUFACTURER="Texas Instruments"