linker: Move iterable subalign value from header to kconfig

Add a Kconfig option for iterable section subalignment.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

Kconfig.zephyr

@@ -316,6 +316,13 @@ config LINKER_USE_RELAX
 
 endmenu # "Linker Sections"
 
+config LINKER_ITERABLE_SUBALIGN
+	int
+	default 8 if 64BIT
+	default 4
+	help
+	  Hidden option for the default subalignment of iterable sections.
+
 config LINKER_DEVNULL_SUPPORT
 	bool
 	default y if CPU_CORTEX_M || (RISCV && !64BIT)

include/zephyr/linker/iterable_sections.h

@@ -32,11 +32,7 @@
 	*(SORT_BY_NAME(._##struct_type.static.*)); \
 	_CONCAT(_##struct_type, _list_end) = .
 
-#ifdef CONFIG_64BIT
-#define Z_LINK_ITERABLE_SUBALIGN  8
-#else
-#define Z_LINK_ITERABLE_SUBALIGN  4
-#endif
+#define Z_LINK_ITERABLE_SUBALIGN CONFIG_LINKER_ITERABLE_SUBALIGN
 
 /**
  * @brief Define a read-only iterable section output.