expression_with_stack_xtensa: renamed and moved assembly helpes of esp_expression_wit_stack to xtensa component

components/xtensa/expression_with_stack_xtensa.S

@@ -0,0 +1,29 @@
+#include    <xtensa/coreasm.h>
+#include    <freertos/xtensa_context.h>
+
+    .text
+/**
+ * extern void switch_stack_enter(portSTACK_TYPE *stack, portSTACK_TYPE *backup_stack);
+ */
+    .globl     esp_switch_stack_enter
+    .type       esp_switch_stack_enter,@function
+    .align      4
+esp_switch_stack_enter:
+    entry   sp, 0x10
+    mov   a4, a1
+    s32i   a4, a3, 0 /* on a3 there is a safe place to save the current stack */
+    l32i   a4, a2, 0 /* obtains the user allocated stack buffer */
+    mov   a1, a4     /* sp register now contains caller specified stack */
+    retw
+
+/**
+ * extern void switch_stack_exit(portSTACK_TYPE *backup_stack);
+ */
+    .globl  esp_switch_stack_exit
+    .type   esp_switch_stack_exit,@function
+    .align  4
+esp_switch_stack_exit:
+    entry   sp, 0x10
+    l32i a4, a2, 0  /* recover the original task stack */
+    mov a1, a4      /* put it on sp register again */
+    retw