usb: vhci-hcd: Prevent suspending virtually attached devices

usb: vhci-hcd: Prevent suspending virtually attached devices

The VHCI platform driver aims to forbid entering system suspend when at
least one of the virtual USB ports are bound to an active USB/IP
connection.

However, in some cases, the detection logic doesn't work reliably, i.e.
when all devices attached to the virtual root hub have been already
suspended, leading to a broken suspend state, with unrecoverable resume.

Ensure the virtually attached devices do not enter suspend by setting
the syscore PM flag.  Note this is currently limited to the client side
only, since the server side doesn't implement system suspend prevention.

Fixes: 04679b3489e0 ("Staging: USB/IP: add client driver")
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250902-vhci-hcd-suspend-fix-v3-1-864e4e833559@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>