drm/radeon: Fix missing prototypes in radeon_atpx_handler.c

Fixes the following gcc with W=1:

drivers/gpu/drm/radeon/radeon_atpx_handler.c:64:6: warning: no previous prototype for ‘radeon_has_atpx’ [-Wmissing-prototypes]
64 | bool 4(void) {
| ^~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:68:6: warning: no previous prototype for ‘radeon_has_atpx_dgpu_power_cntl’ [-Wmissing-prototypes]
68 | bool radeon_has_atpx_dgpu_power_cntl(void) {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:72:6: warning: no previous prototype for ‘radeon_is_atpx_hybrid’ [-Wmissing-prototypes]
72 | bool radeon_is_atpx_hybrid(void) {
| ^~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:77:6: warning: no previous prototype for ‘radeon_atpx_dgpu_req_power_for_displays’ [-Wmissing-prototypes]
77 | bool radeon_atpx_dgpu_req_power_for_displays(void) {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:596:6: warning: no previous prototype for ‘radeon_register_atpx_handler’ [-Wmissing-prototypes]
596 | void radeon_register_atpx_handler(void)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:614:6: warning: no previous prototype for ‘radeon_unregister_atpx_handler’ [-Wmissing-prototypes]
614 | void radeon_unregister_atpx_handler(void)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/radeon/radeon_atpx_handler.c:159: warning: expecting prototype for radeon_atpx_validate_functions(). Prototype was for radeon_atpx_validate() instead

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/radeon: Make radeon_atif_handler static

There are no external users of function radeon_atif_handler so it can
be static.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/radeon: add new ATIF ACPI method

Used for fetching external GPU information.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/radeon: update radeon acpi header

Add some new defs for ATPX.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/radeon: implement handler for ACPI event

Set up an handler for ACPI events and respond to brightness change
requests from the system BIOS.
v2: fix notification when using device-specific command codes
(tested by Pali Rohár <pali.rohar@gmail.com>); cache the encoder
controlling the backlight during the initialization to avoid searching
it every time (suggested by Alex Deucher).
v3: whitespace fixes (Alex Deucher).

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/radeon: add new AMD ACPI header and update relevant code (v2)

Add a new header that defines the AMD ACPI interface used
for laptops, PowerXpress, and chipset specific functionality
and update the current code to use it.

Todo:
- properly verify the ACPI interfaces
- hook up and handle ACPI notifications
- make PX code more robust
- implement PCIe Gen and width switching using ACPI

v2: fix typo in header

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>