drm/solomon: Make DRM_SSD130X depends on MMU

drm/solomon: Make DRM_SSD130X depends on MMU

WARNING: unmet direct dependencies detected for DRM_GEM_SHMEM_HELPER
  Depends on [n]: HAS_IOMEM [=y] && DRM [=m] && MMU [=n]
  Selected by [m]:
  - DRM_SSD130X [=m] && HAS_IOMEM [=y] && DRM [=m]

DRM_GEM_SHMEM_HELPER depends on MMU, DRM_SSD130X should also depends on MMU.

Fixes: 8bab3f281293 ("drm: Add driver for Solomon SSD130x OLED displays")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220312063437.19160-1-yuehaibing@huawei.com