usb: musb: tusb6010: Add tusb_revision to struct musb to store the revision.

Add field to store tusb6010 revision value. Read the revision at
the startup and store to the variable.

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
Signed-off-by: Felipe Balbi <balbi@ti.com>