UPSTREAM: usb: dwc3: gadget: add a pointer to endpoint registers

UPSTREAM: usb: dwc3: gadget: add a pointer to endpoint registers

By adding a pointer to endpoint registers' base
address, we can avoid using our controller-wide
struct dwc3 pointer for everything. At some point
this will allow us to have per-endpoint locks which
will, in turn, let us queue requests to separate
endpoints in parallel.

Because of this change our debugfs interface and io
accessors need to be changed accordingly.

Change-Id: I51229661378e4756f89770e9a813a132b822631c
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>
(cherry picked from commit 2eb8801650b315394ca376a56be2971c867aa9ec)