drm/msm/dp: fix aux-bus EP lifetime

In the Linux kernel, the following vulnerability has been resolved:

drm/msm/dp: fix aux-bus EP lifetime

Device-managed resources allocated post component bind must be tied to

the lifetime of the aggregate DRM device or they will not necessarily be

released when binding of the aggregate device is deferred.

This can lead resource leaks or failure to bind the aggregate device

when binding is later retried and a second attempt to allocate the

resources is made.

For the DP aux-bus, an attempt to populate the bus a second time will

simply fail ("DP AUX EP device already populated").

Fix this by tying the lifetime of the EP device to the DRM device rather

than DP controller platform device.

Patchwork: https://patchwork.freedesktop.org/patch/502672/