usb: dwc3: trace: pretty-print TRB's ctrl field

Improve trb tracing by showing trb flags, interrupts
trb type.

trb flags:
- h - hardware owner of descriptor
- l - last TRB
- c - chain buffers
- s - continue on short packet

interrupt flags:
- s - interrupt on short packet
- c - interrupt on complete

Capital letter means that bit is set, while
lowercase letter means bit is cleared.

Signed-off-by: Janusz Dziedzic <januszx.dziedzic@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>