CVE-2026-74421: drm/rockchip: dw_dp: Switch to drmm_kzalloc()

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

drm/rockchip: dwdp: Switch to drmmkzalloc()

Driver makes use of drmmencoderinit() to initialize the encoder and automatically handle the cleanup by registering drmencodercleanup() with drmmaddaction().

However, the internal structure containing the encoder part gets allocated with devmkzalloc(), which happens while componentbindall() is being called from Rockchip DRM driver. The component framework further ensures it is deallocated as part of releasing all the resources claimed during bind, which is triggered from componentunbindall().

When the reference to the DRM device gets eventually dropped via drmdevput() in rockchipdrmunbind(), drmmencoderallocrelease() attempts to access the now released encoder structure, leading to use-after-free.

Ensure driver's internal structure is still reachable on encoder cleanup by switching from a device-managed allocation to a drm-managed one.