drm/xe: Make xe_gt_freq part of the Documentation

[ Upstream commit 55f8aa083604ce098c9d6a0911c6bcde15d03a80 ]

The documentation was created with the creation of the component,
however it has never been actually shown in the actual Documentation.

While doing this, fixes the identation style, to avoid new warnings
while building htmldocs.

Fixes: bef52b5c7a ("drm/xe: Create a xe_gt_freq component for raw management and sysfs")
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250521165146.39616-3-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
(cherry picked from commit af53f0fd99c3bbb3afd29f1612c9e88c5a92cc01)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Documentation/gpu/xe/index.rst

@@ -16,6 +16,7 @@ DG2, etc is provided to prototype the driver.
    xe_migrate
    xe_cs
    xe_pm
+   xe_gt_freq
    xe_pcode
    xe_gt_mcr
    xe_wa

Documentation/gpu/xe/xe_gt_freq.rst

@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+
+==========================
+Xe GT Frequency Management
+==========================
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_gt_freq.c
+   :doc: Xe GT Frequency Management
+
+Internal API
+============
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_gt_freq.c
+   :internal: