usb: Show charging notification only if power brick is disconnected

On USB HIDL devices (qcom) and barely-implemented AIDL (older Pixels)
the power brick connection status is always POWER_BRICK_STATUS_UNKNOWN,
leading to charging notification showing up even while charging with a
wall charger.

Properly implemented USB AIDL [1] should report
POWER_BRICK_STATUS_DISCONNECTED when charging with anything other than
a wall charger (i.e SDP/PD), hence use this as the check instead.

[1]: https://android.googlesource.com/device/google/gs101/+/94bc87a6f21a027fc8c30ba3fbf1328b0adc5959/usb/usb/Usb.cpp#785

Fixes a13e3779.

Change-Id: I9e251211e5801b2c1766a12bab7d4787c445dc14