drm/i915/hwmon: Get rid of devm

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

drm/i915/hwmon: Get rid of devm

When both hwmon and hwmon drvdata (on which hwmon depends) are device

managed resources, the expectation, on device unbind, is that hwmon will be

released before drvdata. However, in i915 there are two separate code

paths, which both release either drvdata or hwmon and either can be

released before the other. These code paths (for device unbind) are as

follows (see also the bug referenced below):

Call Trace:

release_nodes+0x11/0x70

devres_release_group+0xb2/0x110

component_unbind_all+0x8d/0xa0

component_del+0xa5/0x140

intel_pxp_tee_component_fini+0x29/0x40 [i915]

intel_pxp_fini+0x33/0x80 [i915]

i915_driver_remove+0x4c/0x120 [i915]

i915_pci_remove+0x19/0x30 [i915]

pci_device_remove+0x32/0xa0

device_release_driver_internal+0x19c/0x200

unbind_store+0x9c/0xb0

and

Call Trace:

release_nodes+0x11/0x70

devres_release_all+0x8a/0xc0

device_unbind_cleanup+0x9/0x70

device_release_driver_internal+0x1c1/0x200

unbind_store+0x9c/0xb0

This means that in i915, if use devm, we cannot gurantee that hwmon will

always be released before drvdata. Which means that we have a uaf if hwmon

sysfs is accessed when drvdata has been released but hwmon hasn't.

The only way out of this seems to be do get rid of devm_ and release/free

everything explicitly during device unbind.

v2: Change commit message and other minor code changes

v3: Cleanup from i915_hwmon_register on error (Armin Wolf)

v4: Eliminate potential static analyzer warning (Rodrigo)

Eliminate fetch_and_zero (Jani)

v5: Restore previous logic for ddat_gt->hwmon_dev error return (Andi)