drm/i915/gt: Cleanup spacing of intel_gt_regs.h

There's a lot of inconsistent spacing and indentation in our register
definitions.  Let's clean things up a bit and follow some consistent
rules:

 * "#define" always starts in column 0
 * There's exactly one space between '#define' and the name of a
   register.
 * There's exactly three spaces between '#define' and the name of a
   bit/bitfield.
 * Tabs (no spaces) are used between a definition name and its value;
   the value starts on column 48 unless the name is too long, in which
   case a single tab is used.

Final diff for this patch is empty if whitespace is ignored:

        $ git diff -w
        $
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209051140.1599643-5-matthew.d.roper@intel.com