drm/sprd: remove the selected DRM_KMS_CMA_HELPER in kconfig

On commit 43531edd ("drm/sprd: add Unisoc's drm kms master"),
adds the config DRM_SPRD, which selects DRM_KMS_CMA_HELPER.

However, commit 09717af7 ("drm: Remove CONFIG_DRM_KMS_CMA_HELPER
option") just removed the DRM_KMS_CMA_HELPER.
So the select DRM_KMS_CMA_HELPER refers to a non-existing kconfig symbol.
Reported-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Kevin Tang <kevin3.tang@gmail.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/all/20220117083820.6893-2-kevin3.tang@gmail.com

v1 -> v2:
- fix commit comments long lines issue and drop "On linux-next" comments

drivers/gpu/drm/sprd/Kconfig

@@ -3,7 +3,6 @@ config DRM_SPRD
 	depends on ARCH_SPRD || COMPILE_TEST
 	depends on DRM && OF
 	select DRM_GEM_CMA_HELPER
-	select DRM_KMS_CMA_HELPER
 	select DRM_KMS_HELPER
 	select DRM_MIPI_DSI
 	select VIDEOMODE_HELPERS