[nrf fromlist] kernel: Guard SYS_CLOCK_HW_CYCLES_PER_SEC to avoid spurious empty macro

If SYS_CLOCK_EXISTS is not enabled, then the SYS_CLOCK_HW_CYCLES_PER_SEC
still gets created, but with no value. This causes the code generation
in misc/generated/CMakeLists.txt to create an empty assembly macro:

`.equ  CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC,`

which then causes a build error.

Disable the Kconfig option entirely when SYS_CLOCK_EXISTS is disabled to
fix this.

This is a follow-up to 03f46db.

Upstream PR #: 91179

Signed-off-by: Carles Cufi <[email protected]>

Author: carlescufi

kernel/Kconfig

@@ -826,13 +826,15 @@ config SYS_CLOCK_TICKS_PER_SEC
 
 	  A value of 0 completely disables timer support in the kernel.
 
+if SYS_CLOCK_EXISTS
 config SYS_CLOCK_HW_CYCLES_PER_SEC
 	int "System clock's h/w timer frequency"
 	default 0 if TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
 	help
 	  This option specifies the frequency of the hardware timer used for the
 	  system clock (in Hz). This option is set by the SOC's or board's Kconfig file
 	  and the user should generally avoid modifying it via the menu configuration.
+endif
 
 config SYS_CLOCK_EXISTS
 	bool "System clock exists and is enabled"