clock: Remove CONFIG_TICKLESS_KERNEL_TIME_UNIT_IN_MICRO_SECS

This was only used in a few places just to indirect the already
perfectly valid SYS_CLOCK_TICKS_PER_SEC value.  There's no reason for
these to ever have been kconfig units, and in fact the distinction
appears to have introduced a hidden/untested bug in the power
subsystem (the two variables were used interchangably, but they were
defined in reciprocal units!).

Just use "ticks" as our time unit pervasively, and clarify the docs to
explain that.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

include/sys_clock.h

@@ -28,11 +28,7 @@ extern "C" {
 
 static inline int sys_clock_ticks_per_sec(void)
 {
-#ifdef CONFIG_TICKLESS_KERNEL
-	return 1000000 / (CONFIG_TICKLESS_KERNEL_TIME_UNIT_IN_MICRO_SECS);
-#else
 	return CONFIG_SYS_CLOCK_TICKS_PER_SEC;
-#endif
 }
 
 #ifdef CONFIG_TICKLESS_KERNEL

kernel/Kconfig

@@ -516,6 +516,11 @@ config SYS_CLOCK_TICKS_PER_SEC
 	  can require a non-trivial extra amount of stack space (e.g. around 80
 	  bytes on x86).
 
+	  Note that when available and enabled, in "tickless" mode
+	  this config variable specifies the minimum available timing
+	  granularity, not necessarily the number or frequency of
+	  interrupts delivered to the kernel.
+
 config SYS_CLOCK_HW_CYCLES_PER_SEC
 	int "System clock's h/w timer frequency"
 	help

kernel/Kconfig.power_mgmt

@@ -97,18 +97,6 @@ config TICKLESS_KERNEL
 	  clock interrupt generation would be stopped at all times. This option
 	  requires Tickless Idle option to be enabled.
 
-config TICKLESS_KERNEL_TIME_UNIT_IN_MICRO_SECS
-	int "Tickless kernel time unit in micro seconds"
-	default 1000
-	depends on TICKLESS_KERNEL
-	help
-	  This option makes the system clock and scheduling granularity.
-	  The default will be one millisecond. This option also determines
-	  the time unit passed in functions like _sys_soc_suspend. The
-	  value should be determined based what the timer hardware and driver
-	  can support. Specifying too small a time unit than what the overall
-	  system speed can support would cause scheduling errors.
-
 config BUSY_WAIT_USES_ALTERNATE_CLOCK
 	bool "Busy wait uses alternate clock in tickless kernel mode"
 	help

subsys/power/policy/policy_residency.c

@@ -13,11 +13,7 @@
 #include <logging/log.h>
 LOG_MODULE_DECLARE(power);
 
-#ifdef CONFIG_TICKLESS_KERNEL
-#define SECS_TO_TICKS		CONFIG_TICKLESS_KERNEL_TIME_UNIT_IN_MICRO_SECS
-#else
 #define SECS_TO_TICKS		CONFIG_SYS_CLOCK_TICKS_PER_SEC
-#endif
 
 #if !(defined(CONFIG_SYS_POWER_STATE_CPU_LPS_SUPPORTED) || \
 		defined(CONFIG_SYS_POWER_STATE_CPU_LPS_1_SUPPORTED) || \