libc: common: Fix init hang issue

In device init phase, it will call _mbedtls_init before malloc_prepare
as mbedtls has higher priority defined in SYS_INIT..
_mbedtls_init() will call psa_crypto_init() and malloc buffer,
but z_malloc_heap is not initialized, which will cause device hang.
Should call malloc_prepare() before _mbedtls_init to fix this issue,
so add new Kconfig to increase the priority of libc to deafult 30.

Signed-off-by: Maochen Wang <maochen.wang@nxp.com>

kernel/Kconfig.device

@@ -45,6 +45,14 @@ config KERNEL_INIT_PRIORITY_OBJECTS
 	  priority needs to be higher than minimal default initialization
 	  priority.
 
+config KERNEL_INIT_PRIORITY_LIBC
+	int "LIBC initialization priority"
+	default 35
+	help
+	  LIBC uses this priority for initialization. This
+	  priority needs to be higher than minimal default initialization
+	  priority.
+
 config KERNEL_INIT_PRIORITY_DEFAULT
 	int "Default init priority"
 	default 40

lib/libc/common/source/stdlib/malloc.c

@@ -260,7 +260,7 @@ void free(void *ptr)
 	malloc_unlock();
 }
 
-SYS_INIT(malloc_prepare, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
+SYS_INIT(malloc_prepare, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_LIBC);
 #else /* No malloc arena */
 void *malloc(size_t size)
 {

lib/libc/newlib/libc-hooks.c

@@ -142,7 +142,7 @@ static int malloc_prepare(void)
 	return 0;
 }
 
-SYS_INIT(malloc_prepare, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
+SYS_INIT(malloc_prepare, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_LIBC);
 
 /* Current offset from HEAP_BASE of unused memory */
 LIBC_BSS static size_t heap_sz;