Documentation: intel_pstate: fix duplicate hyperlink target errors

Fix reST warnings in
Documentation/admin-guide/pm/intel_pstate.rst caused by missing explicit
hyperlink labels for section titles.

Before this change, the following errors were printed during
`make htmldocs`:

Documentation/admin-guide/pm/intel_pstate.rst:401:
ERROR: Indirect hyperlink target (id="id6") refers to target
"passive mode", which is a duplicate, and cannot be used as a
unique reference.
Documentation/admin-guide/pm/intel_pstate.rst:517:
ERROR: Indirect hyperlink target (id="id9") refers to target
"active mode", which is a duplicate, and cannot be used as a
unique reference.
Documentation/admin-guide/pm/intel_pstate.rst:611:
ERROR: Indirect hyperlink target (id="id15") refers to target
"global attributes", which is a duplicate, and cannot be used as
a unique reference.
ERROR: Duplicate target name, cannot be used as a unique reference:
"passive mode", "active mode", "global attributes".

These errors occurred because the sections "Active Mode",
"Active Mode With HWP", "Passive Mode", and "Global Attributes"
did not define explicit hyperlink labels. As a result, Sphinx
auto-generated duplicate anchors when the same titles appeared
multiple times within the document.

Because of this, the generated HTML documentation contained
broken references such as:

`active mode <Active Mode_>`_
`passive mode <Passive Mode_>`_
`global attributes <Global Attributes_>`_

This patch adds explicit hyperlink labels for the affected sections,
ensuring all references are unique and correctly resolved.

After applying this patch, `make htmldocs` completes without
any warnings, and all hyperlinks in intel_pstate.html render properly.

Signed-off-by: Swaraj Gaikwad <[e-mail]>
Reviewed-by: Bagas Sanjaya <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]>
[ rjw: Subject adjustment ]
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/admin-guide/pm/intel_pstate.rst

···
 depends on what kernel command line options are used and on the capabilities of
 the processor.
 
+.. _Active Mode:
+
 Active Mode
 -----------
 
···
 :c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option.
 Namely, if that option is set, the ``performance`` algorithm will be used by
 default, and the other one will be used by default if it is not set.
+
+.. _Active Mode With HWP:
 
 Active Mode With HWP
 ~~~~~~~~~~~~~~~~~~~~
···
 This is the default P-state selection algorithm if the
 :c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option
 is not set.
+
+.. _Passive Mode:
 
 Passive Mode
 ------------
···
 
 User Space Interface in ``sysfs``
 =================================
+
+.. _Global Attributes:
 
 Global Attributes
 -----------------