drm/radeon: align short build log

This beautifies the build log.

[Before]

  HOSTCC  drivers/gpu/drm/radeon/mkregtable
  MKREGTABLE drivers/gpu/drm/radeon/r100_reg_safe.h
  MKREGTABLE drivers/gpu/drm/radeon/rn50_reg_safe.h
  CC [M]  drivers/gpu/drm/radeon/r100.o
  MKREGTABLE drivers/gpu/drm/radeon/r300_reg_safe.h
  CC [M]  drivers/gpu/drm/radeon/r300.o

[After]

  HOSTCC  drivers/gpu/drm/radeon/mkregtable
  MKREG   drivers/gpu/drm/radeon/r100_reg_safe.h
  MKREG   drivers/gpu/drm/radeon/rn50_reg_safe.h
  CC [M]  drivers/gpu/drm/radeon/r100.o
  MKREG   drivers/gpu/drm/radeon/r300_reg_safe.h
  CC [M]  drivers/gpu/drm/radeon/r300.o

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>