UPSTREAM: usb: gadget: udc: core: Revise comments for USB ep enable/disable

The usb_ep_disable() and usb_ep_enable() routines are being widely
used in atomic/interrupt context by function drivers.  Hence, the
statement about it being able to only run in process context may
not be true.  Add an explicit comment mentioning that it can be used
in atomic context.

Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>

Bug: 204343836
(cherry picked from commit b0d5d2a7)
Change-Id: I1adb5d074fe2f9e33ebfdb30d335283c56bc7b39
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>