drm_mipi_dbi needs lots of DRM_KMS_HELPER support, so select
that Kconfig symbol like it is done is most other uses, and
the way that it was before MIPS_DBI was moved from tinydrm
to its core location.

Fixes these build errors:

ld: drivers/gpu/drm/drm_mipi_dbi.o: in function `mipi_dbi_buf_copy':
drivers/gpu/drm/drm_mipi_dbi.c:205: undefined reference to `drm_gem_fb_get_obj'
ld: drivers/gpu/drm/drm_mipi_dbi.c:211: undefined reference to `drm_gem_fb_begin_cpu_access'
ld: drivers/gpu/drm/drm_mipi_dbi.c:215: undefined reference to `drm_gem_fb_vmap'
ld: drivers/gpu/drm/drm_mipi_dbi.c:222: undefined reference to `drm_fb_swab'
ld: drivers/gpu/drm/drm_mipi_dbi.c:224: undefined reference to `drm_fb_memcpy'
ld: drivers/gpu/drm/drm_mipi_dbi.c:227: undefined reference to `drm_fb_xrgb8888_to_rgb565'
ld: drivers/gpu/drm/drm_mipi_dbi.c:235: undefined reference to `drm_gem_fb_vunmap'
ld: drivers/gpu/drm/drm_mipi_dbi.c:237: undefined reference to `drm_gem_fb_end_cpu_access'
ld: drivers/gpu/drm/drm_mipi_dbi.o: in function `mipi_dbi_dev_init_with_formats':
ld: drivers/gpu/drm/drm_mipi_dbi.o:/X64/../drivers/gpu/drm/drm_mipi_dbi.c:469: undefined reference to `drm_gem_fb_create_with_dirty'

Fixes: 174102f4 ("drm/tinydrm: Move mipi-dbi")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Dillon Min <dillon.minfei@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220823004243.11596-1-rdunlap@infradead.org