Improve perfmon json table picker

Built a tool to chew up https://download.01.org/perfmon/mapfile.csv,
and output a table in this format:

typedef struct {
  u8 model;
  u8 stepping;
  u8 has_stepping;
  char *filename;
} file_by_model_and_stepping_t;

static const file_by_model_and_stepping_t fms_table [] =
{
 /* model, stepping, stepping valid, file */
  { 0x2E, 0x0, 0, "NehalemEX_core_V2.json" },
  { 0x1E, 0x0, 0, "NehalemEP_core_V2.json" },
<snip>
  { 0x55, 0x5, 1, "cascadelakex_core_v1.00.json" },
  { 0x55, 0x6, 1, "cascadelakex_core_v1.00.json" },
  { 0x55, 0x7, 1, "cascadelakex_core_v1.00.json" },
<snip>

Change-Id: Ie0e8a7e851799e9d060b966047745039c066ec7b
Signed-off-by: Dave Barach <dave@barachs.net>