usb: musb: tusb-dma can't be built-in if tusb is not

A configuration with CONFIG_USB_MUSB_HDRC=y, CONFIG_USB_TUSB_OMAP_DMA=y
and CONFIG_USB_MUSB_TUSB6010=m causes a link failure because of the
dependency on the tusb_get_revision symbol:

(.text+0x154ce8): undefined reference to `tusb_get_revision'

This patch ensures that either MUSB_HDRC and MUSB_TUSB6010 are
both modules or both built-in, which are the valid configurations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>