perf trace beauty: Default header_dir to cwd to work without parms

perf trace beauty: Default header_dir to cwd to work without parms

Useful when checking the effects of header synchs for the files it uses
as a input to generate string tables, in retrospect this is how it
should've been done from day 1, not requiring the header_dir to be set
on the Makefile, will change everything later, so that the only parm,
common to all generators will be $(srctree) and $(beauty_outdir).

So, to see what it generates, just call it without any parameters:

  $ tools/perf/trace/beauty/vhost_virtio_ioctl.sh
  static const char *vhost_virtio_ioctl_cmds[] = {
	[0x00] = "SET_FEATURES",
	[0x01] = "SET_OWNER",
	[0x02] = "RESET_OWNER",
	[0x03] = "SET_MEM_TABLE",
	[0x04] = "SET_LOG_BASE",
	[0x07] = "SET_LOG_FD",
	[0x10] = "SET_VRING_NUM",
	[0x11] = "SET_VRING_ADDR",
	[0x12] = "SET_VRING_BASE",
	[0x13] = "SET_VRING_ENDIAN",
	[0x14] = "GET_VRING_ENDIAN",
	[0x20] = "SET_VRING_KICK",
	[0x21] = "SET_VRING_CALL",
	[0x22] = "SET_VRING_ERR",
	[0x23] = "SET_VRING_BUSYLOOP_TIMEOUT",
	[0x24] = "GET_VRING_BUSYLOOP_TIMEOUT",
	[0x30] = "NET_SET_BACKEND",
	[0x40] = "SCSI_SET_ENDPOINT",
	[0x41] = "SCSI_CLEAR_ENDPOINT",
	[0x42] = "SCSI_GET_ABI_VERSION",
	[0x43] = "SCSI_SET_EVENTS_MISSED",
	[0x44] = "SCSI_GET_EVENTS_MISSED",
	[0x60] = "VSOCK_SET_GUEST_CID",
	[0x61] = "VSOCK_SET_RUNNING",
  };
  static const char *vhost_virtio_ioctl_read_cmds[] = {
	[0x00] = "GET_FEATURES",
	[0x12] = "GET_VRING_BASE",
  };
  $

Or:

  $ tools/perf/trace/beauty/sndrv_pcm_ioctl.sh
  static const char *sndrv_pcm_ioctl_cmds[] = {
	[0x00] = "PVERSION",
	[0x01] = "INFO",
	[0x02] = "TSTAMP",
	[0x03] = "TTSTAMP",
	[0x04] = "USER_PVERSION",
	[0x10] = "HW_REFINE",
	[0x11] = "HW_PARAMS",
	[0x12] = "HW_FREE",
	[0x13] = "SW_PARAMS",
	[0x20] = "STATUS",
	[0x21] = "DELAY",
	[0x22] = "HWSYNC",
	[0x23] = "SYNC_PTR",
	[0x24] = "STATUS_EXT",
	[0x32] = "CHANNEL_INFO",
	[0x40] = "PREPARE",
	[0x41] = "RESET",
	[0x42] = "START",
	[0x43] = "DROP",
	[0x44] = "DRAIN",
	[0x45] = "PAUSE",
	[0x46] = "REWIND",
	[0x47] = "RESUME",
	[0x48] = "XRUN",
	[0x49] = "FORWARD",
	[0x50] = "WRITEI_FRAMES",
	[0x51] = "READI_FRAMES",
	[0x52] = "WRITEN_FRAMES",
	[0x53] = "READN_FRAMES",
	[0x60] = "LINK",
	[0x61] = "UNLINK",
  };
  $

Etc.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-90am4vm8hh1osms894dp2otr@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>