current mod_host used usbhs_device_alloc/free(),
but allocated variable was attached to each xx->hcpriv.
The intuitively clear name was not xxx_alloc/free() but xxx_attach/detach().

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>