drm/display: move CEC_CORE selection to DRM_DISPLAY_HELPER

THe Kconfig symbol DRM_DISPLAY_DP_AUX_CEC is a boolean which simply
toggles whether DP_AUX_CEC support should be built into the
drm_display_helper (which can be eithera module or built-in into the
kernel). If DRM_DISPLAY_DP_AUX_CEC is selected, then CEC_CORE is
selected to be built-in into the kernel even if DRM_DISPLAY_HELPER is
selected to be built as a module. Move CEC_CORE selection to the latter
symbol in order to allow it to be built as a module.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250517-drm-hdmi-connector-cec-v6-4-35651db6f19b@oss.qualcomm.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>