kernel: Drop non-standard GNU inline assignment syntax

* We needed this previously due to our gcc2 compiled kernel.
* Now that our kernel is always latest gcc, we can move to the
c++20 syntax for inline assignment.
* Improves compatibility with clang, less GNU-specific stuff

Change-Id: Ib7272a0a52554a31e9a0e788fd3f031db9049795
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5898
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Add Todos for adapter and displays.

WIP ACPI display adapters driver

Currently find display adapters and attached displays but nothing more.
I would like it to publish adapters and displays in dev tree, so that
you can open and control the adapter (get firmware, boot display) and
the adapter itself would have child devices for displays (brightness ..).

However that part could use some review, and since my time is limited it
is better to make it availble for others to work on as well.

Format code, add display device base.

Still very much work in progress.

Rename display_controls to display_adapter

ACPI talks about display_adapters, and we will likely have displays
as child nodes. Displays will be attached to an adapter.

Add Todos for adapter and displays.

WIP ACPI display adapters driver

Currently find display adapters and attached displays but nothing more.
I would like it to publish adapters and displays in dev tree, so that
you can open and control the adapter (get firmware, boot display) and
the adapter itself would have child devices for displays (brightness ..).

However that part could use some review, and since my time is limited it
is better to make it availble for others to work on as well.

Format code, add display device base.

Still very much work in progress.

Rename display_controls to display_adapter

ACPI talks about display_adapters, and we will likely have displays
as child nodes. Displays will be attached to an adapter.