usb: gadget: introduce 'enabled' flag in struct usb_ep

usb: gadget: introduce 'enabled' flag in struct usb_ep

f_acm calls usb_ep_disable(f_acm->ep_notify) unconditionally in
acm_start_ctrl(), even if the USB endpoint was never enabled before. This
causes crashes for some UDC drivers (e.g. ci_udc), because they dereference
data structures that are assigned only after having called usb_ep_enable().

The f_acm driver in U-Boot is similar to the Linux driver, where this issue
does not occur because usb_ep_disable() and usb_ep_enable() internally
track the enabled state. In Linux this change was made in commit
b0bac2581c19 ("usb: gadget: introduce 'enabled' flag in struct usb_ep") by
Robert Baldyga.

Fix the crashes for f_acm by making the same change in U-Boot. This makes
the API less bug-prone and avoids introducing crashes when adapting new
gadget drivers from Linux.

Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Link: https://lore.kernel.org/r/20250407-acm-fixes-v1-3-e3dcb592d6d6@linaro.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>