drm/i915/i915_reg.h: fix the checkpatch SPACE_BEFORE_TAB issues

Since I'm touching the file I might as well fix this class of errors
since they are just a few. Also drive-by fix the styling of the
VLV_TURBO_SOC_OVERRIDE definitions instead of just the spaces before
the tabs.
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180612235654.7914-3-paulo.r.zanoni@intel.com