Revert "drm: Switch DRM_DISPLAY_DP_HELPER to depends on"

This reverts commit 0323287d, as helper
code should always be selected by the driver that needs it, for the
convenience of the final user configuring a kernel.

The user who configures a kernel should not need to know which helpers
are needed for the driver he is interested in.  Making a driver depend
on helper code means that the user needs to know which helpers to enable
first, which is very user-unfriendly.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patchwork.freedesktop.org/patch/msgid/89ac456805746b6d0c888f10c5120b11aacd3319.1713780345.git.geert+renesas@glider.be


Signed-off-by: Maxime Ripard <mripard@kernel.org>