usb: musb: add tracepoints for register access

This adds tracepoints to musb register read/write wrappers to get
trace log for register access.

The default tacepoint log prefix here would be musb_readX/writeX(),
which is not much helpful. So this patch let the tracepoints use
__buildin_return_address(0) to print the caller funciton name to
provide more context of the register access.

Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>