drm/amd: Allow s0ix without BIOS support

We guard the suspend entry code from running unless we have proper
BIOS support for either S3 mode or s0ix mode.

If a user's system doesn't support either of these modes the kernel
still does offer s2idle in `/sys/power/mem_sleep` so there is an
expectation from users that it works even if the power consumption
remains very high.

Rafael Ávila de Espíndola reports that a system of his has a
non-functional graphics stack after resuming.  That system doesn't
support S3 and the FADT doesn't indicate support for low power idle.

Through some experimentation it was concluded that even without the
hardware s0i3 support provided by the amd_pmc driver the power
consumption over suspend is decreased by running amdgpu's s0ix
suspend routine.

The numbers over suspend showed:
* No patch: 9.2W
* Skip amdgpu suspend entirely: 10.5W
* Run amdgpu s0ix routine: 7.7W

As this does improve the power, remove some of the guard rails in
`amdgpu_acpi.c` for only running s0ix suspend routines in the right
circumstances.

However if this turns out to cause regressions for anyone, we should
revert this change and instead opt for skipping suspend/resume routines
entirely or try to fix the underlying behavior that makes graphics fail
after resume without underlying platform support.
Reported-by: Rafael Ávila de Espíndola <rafael@espindo.la>
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2364Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c

@@ -1079,20 +1079,16 @@ bool amdgpu_acpi_is_s0ix_active(struct amdgpu_device *adev)
 	 * S0ix even though the system is suspending to idle, so return false
 	 * in that case.
 	 */
-	if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
+	if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
 		dev_warn_once(adev->dev,
 			      "Power consumption will be higher as BIOS has not been configured for suspend-to-idle.\n"
 			      "To use suspend-to-idle change the sleep mode in BIOS setup.\n");
-		return false;
-	}
 
 #if !IS_ENABLED(CONFIG_AMD_PMC)
 	dev_warn_once(adev->dev,
 		      "Power consumption will be higher as the kernel has not been compiled with CONFIG_AMD_PMC.\n");
-	return false;
-#else
-	return true;
 #endif /* CONFIG_AMD_PMC */
+	return true;
 }
 
 #endif /* CONFIG_SUSPEND */