drm/i915/gvt: rewrite the trace gvt:gvt_command using trace style approach

drm/i915/gvt: rewrite the trace gvt:gvt_command using trace style approach

The gvt:gvt_command trace involve unnecessary overhead even this trace is
not enabled. We need improve it.

The kernel trace infrastructure provide a full api to define a trace event.
We should leverage them if possible. And one important thing is that a trace
point should store raw data but not format string.

This patch include two part work:
1) Refactor the gvt_command trace definition, including:
  o only store raw trace data.
  o use __dynamic_array() to declare a variable size buffer.
  o use __print_array() to format raw cmd data.
  o rename vm_id as vgpu_id.

2) Improve the trace invoking, including:
  o remove the cycles calculation for handler. We can get this data
    by any perf tool.
  o do not make a backup for raw cmd data which just doesn't make sense.

With this patch, this trace has no overhead if it is not enabled. And we are
trace style now.

The final output example:
  gvt workload 0-211   [000] ...1   120.555964: gvt_command: vgpu1 ring 0: buf_type 0, ip_gma e161e880, raw cmd {0x4000000}
  gvt workload 0-211   [000] ...1   120.556014: gvt_command: vgpu1 ring 0: buf_type 0, ip_gma e161e884, raw cmd {0x7a000004,0x1004000,0xe1511018,0x0,0x7d,0x0}
  gvt workload 0-211   [000] ...1   120.556062: gvt_command: vgpu1 ring 0: buf_type 0, ip_gma e161e89c, raw cmd {0x7a000004,0x140000,0x0,0x0,0x0,0x0}
  gvt workload 0-211   [000] ...1   120.556110: gvt_command: vgpu1 ring 0: buf_type 0, ip_gma e161e8b4, raw cmd {0x10400002,0xe1511018,0x0,0x7d}

Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>