change(xtensa): Deprecate ".../xtensa_api.h" include path

This commit deprecates the "freertos/xtensa_api.h" and "xtensa/xtensa_api.h"
include paths. Users should use "xtensa_api.h" instead.

- Replace legacy include paths
- Removed some unnecessary includes of "xtensa_api.h"
- Replaced some calls with "esp_cpu_..." equivalents
- Add warning to compatibility header

components/esp_hw_support/include/esp_cpu.h

@@ -12,7 +12,7 @@
 #include <assert.h>
 #include "soc/soc_caps.h"
 #ifdef __XTENSA__
-#include "xtensa/xtensa_api.h"
+#include "xtensa_api.h"
 #include "xt_utils.h"
 #elif __riscv
 #include "riscv/rv_utils.h"