xtensa: introduce prep_c for xtensa

xtensa is the only architecutre doing thing differently and introduces
inconsistency in the init process and dependencies as we attemp to
cleanup init levels and remove misused of SYS_INIT.

Introduce prep_c for this architecture and align with other
architectures.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

arch/xtensa/core/CMakeLists.txt

@@ -12,6 +12,7 @@ zephyr_library_sources(
   irq_manage.c
   thread.c
   vector_handlers.c
+  prep_c.c
   )
 
 zephyr_library_sources_ifdef(CONFIG_XTENSA_USE_CORE_CRT1 crt1.S)

arch/xtensa/core/crt1.S

@@ -22,7 +22,7 @@
  */
 
 .global __start
-.type	z_cstart, @function
+.type	z_prep_c, @function
 
 
 /* Macros to abstract away ABI differences */
@@ -189,6 +189,6 @@ _start:
 #endif /* !XCHAL_HAVE_BOOTLOADER */
 
 	/* Enter C domain, never returns from here */
-	CALL	z_cstart
+	CALL	z_prep_c
 
 	.size	_start, . - _start

arch/xtensa/core/prep_c.c

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2024 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <zephyr/kernel.h>
+#include <kernel_internal.h>
+
+extern FUNC_NORETURN void z_cstart(void);
+
+/**
+ *
+ * @brief Prepare to and run C code
+ *
+ * This routine prepares for the execution of and runs C code.
+ *
+ */
+void z_prep_c(void)
+{
+	z_cstart();
+	CODE_UNREACHABLE;
+}