cpufreq: Drop unused symbol CPUFREQ_ETERNAL

Drop CPUFREQ_ETERNAL that has no users any more along with all
references to it in the documentation.

No functional impact.

Reviewed-by: Mario Limonciello (AMD) <[e-mail]>
Reviewed-by: Jie Zhan <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Reviewed-by: Qais Yousef <[e-mail]>

Documentation/admin-guide/pm/cpufreq.rst

···
 	The time it takes to switch the CPUs belonging to this policy from one
 	P-state to another, in nanoseconds.
 
-	If unknown or if known to be so high that the scaling driver does not
-	work with the `ondemand`_ governor, -1 (:c:macro:`CPUFREQ_ETERNAL`)
-	will be returned by reads from this attribute.
-
 ``related_cpus``
 	List of all (online and offline) CPUs belonging to this policy.
 

Documentation/cpu-freq/cpu-drivers.rst

···
 +-----------------------------------+--------------------------------------+
 |policy->cpuinfo.transition_latency | the time it takes on this CPU to	   |
 |				    | switch between two frequencies in	   |
-|				    | nanoseconds (if appropriate, else	   |
-|				    | specify CPUFREQ_ETERNAL)		   |
+|				    | nanoseconds                          |
 +-----------------------------------+--------------------------------------+
 |policy->cur			    | The current operating frequency of   |
 |				    | this CPU (if appropriate)		   |

Documentation/translations/zh_CN/cpu-freq/cpu-drivers.rst

···
 |                                   |                                      |
 +-----------------------------------+--------------------------------------+
 |policy->cpuinfo.transition_latency | CPU在两个频率之间切换所需的时间，以  |
-|                                   | 纳秒为单位（如不适用，设定为         |
-|                                   | CPUFREQ_ETERNAL）                    |
+|                                   | 纳秒为单位                    |
 |                                   |                                      |
 +-----------------------------------+--------------------------------------+
 |policy->cur                        | 该CPU当前的工作频率(如适用)          |

Documentation/translations/zh_TW/cpu-freq/cpu-drivers.rst

···
 |                                   |                                      |
 +-----------------------------------+--------------------------------------+
 |policy->cpuinfo.transition_latency | CPU在兩個頻率之間切換所需的時間，以  |
-|                                   | 納秒爲單位（如不適用，設定爲         |
-|                                   | CPUFREQ_ETERNAL）                    |
+|                                   | 納秒爲單位                    |
 |                                   |                                      |
 +-----------------------------------+--------------------------------------+
 |policy->cur                        | 該CPU當前的工作頻率(如適用)          |

include/linux/cpufreq.h

···
  *********************************************************************/
 /*
  * Frequency values here are CPU kHz
- *
- * Maximum transition latency is in nanoseconds - if it's unknown,
- * CPUFREQ_ETERNAL shall be used.
  */
-
-#define CPUFREQ_ETERNAL			(-1)
 
 #define CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS	NSEC_PER_MSEC