drm/<drivers>: Constify struct drm_driver

Only the following drivers aren't converted:
- amdgpu, because of the driver_feature mangling due to virt support.
  Subsequent patch will address this.
- nouveau, because DRIVER_ATOMIC uapi is still not the default on the
  platforms where it's supported (i.e. again driver_feature mangling)
- vc4, again because of driver_feature mangling
- qxl, because the ioctl table is somewhere else and moving that is
  maybe a bit too much, hence the num_ioctls assignment prevents a
  const driver structure.
- arcpgu, because that is stuck behind a pending tiny-fication series
  from me.
- legacy drivers, because legacy requires non-const drm_driver.

Note that for armada I also went ahead and made the ioctl array const.

Only cc'ing the driver people who've not been converted (everyone else
is way too much).

v2: Fix one misplaced const static, should be static const (0day)

v3:
- Improve commit message (Sam)

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: kernel test robot <lkp@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201104100425.1922351-5-daniel.vetter@ffwll.ch