usb: dwc3: trace: decode ctrl request

Instead of *always* dumping raw ctrl bytes, let's decode standard
requests which will make the lives of those debugging DWC3 quite a bit
easier.

Output will now look like so:

irq/34-dwc3-1594  [000] d..1   107.573081: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   107.573694: dwc3_ctrl_req: Set Address(Addr = 01)
irq/34-dwc3-1594  [000] d..1   107.588319: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   107.588816: dwc3_ctrl_req: Get Configuration Descriptor(Index = 0, Length = 9)
irq/34-dwc3-1594  [000] d..1   107.589191: dwc3_ctrl_req: Set Configuration(Config = 3)
irq/34-dwc3-1594  [000] d..1   107.589846: dwc3_ctrl_req: Get BOS Descriptor(Index = 0, Length = 5)
irq/34-dwc3-1594  [000] d..1   107.590146: dwc3_ctrl_req: Get BOS Descriptor(Index = 0, Length = 22)
irq/34-dwc3-1594  [000] d..1   107.590546: dwc3_ctrl_req: Get Configuration Descriptor(Index = 0, Length = 9)
irq/34-dwc3-1594  [000] d..1   107.590840: dwc3_ctrl_req: Get Configuration Descriptor(Index = 0, Length = 69)
irq/34-dwc3-1594  [000] d..1   107.591138: dwc3_ctrl_req: Get Configuration Descriptor(Index = 1, Length = 9)
irq/34-dwc3-1594  [000] d..1   107.591541: dwc3_ctrl_req: Get Configuration Descriptor(Index = 1, Length = 32)
irq/34-dwc3-1594  [000] d..1   107.591834: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   114.701005: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   114.721080: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   114.722709: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   114.728979: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   114.730544: dwc3_ctrl_req: Get Device Qualifier Descriptor(Index = 0, Length = 10)
irq/34-dwc3-1594  [000] d..1   115.776018: dwc3_ctrl_req: Get Configuration Descriptor(Index = 0, Length = 9)
irq/34-dwc3-1594  [000] d..1   115.776760: dwc3_ctrl_req: Set Configuration(Config = 0)
irq/34-dwc3-1594  [000] d..1   115.777676: dwc3_ctrl_req: Get Configuration(Length = 1)
irq/34-dwc3-1594  [000] d..1   115.924797: dwc3_ctrl_req: Get Device Descriptor(Index = 0, Length = 18)
irq/34-dwc3-1594  [000] d..1   115.929025: dwc3_ctrl_req: Get String Descriptor(Index = 0, Length = 500)
irq/34-dwc3-1594  [000] d..1   115.929566: dwc3_ctrl_req: Get String Descriptor(Index = 1, Length = 500)
irq/34-dwc3-1594  [000] d..1   115.930911: dwc3_ctrl_req: Get String Descriptor(Index = 0, Length = 500)
irq/34-dwc3-1594  [000] d..1   115.931528: dwc3_ctrl_req: Get String Descriptor(Index = 2, Length = 500)
irq/34-dwc3-1594  [000] d..1   115.932950: dwc3_ctrl_req: Get String Descriptor(Index = 0, Length = 500)
irq/34-dwc3-1594  [000] d..1   115.933533: dwc3_ctrl_req: Get String Descriptor(Index = 3, Length = 500)

Note that Class and Vendor requests won't be decoded for obvious
reasons. Those will be printed as a raw sequence of bytes.

This patch has been tested against a normal host (both Linux and
Windows) and USB30CV Chapter 9 tests.

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