Convert CONFIG_USB_MUSB_OMAP2PLUS et al to Kconfig

This converts the following to Kconfig:
   CONFIG_USB_MUSB_OMAP2PLUS
   CONFIG_USB_MUSB_AM35X
   CONFIG_USB_MUSB_DSPS
   CONFIG_USB_MUSB_PIO_ONLY

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/am335x_evm_usbspl_defconfig b/configs/am335x_evm_usbspl_defconfig
index 1e80017..10d6d38 100644
--- a/configs/am335x_evm_usbspl_defconfig
+++ b/configs/am335x_evm_usbspl_defconfig
@@ -38,6 +38,7 @@
 CONFIG_USB=y
 CONFIG_USB_MUSB_HOST=y
 CONFIG_USB_MUSB_GADGET=y
+CONFIG_USB_MUSB_DSPS=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_GADGET_MANUFACTURER="Texas Instruments"