xtensa: extract common CPU reset code into separate function

platform_restart implementatations do the same thing to reset CPU.
Don't duplicate that code, move it to a function and call it from
platform_restart.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/platforms/iss/setup.c b/arch/xtensa/platforms/iss/setup.c
index 3918205..e29e1b4 100644
--- a/arch/xtensa/platforms/iss/setup.c
+++ b/arch/xtensa/platforms/iss/setup.c
@@ -53,25 +53,7 @@
 {
 	/* Flush and reset the mmu, simulate a processor reset, and
 	 * jump to the reset vector. */
-
-	__asm__ __volatile__("movi	a2, 15\n\t"
-			     "wsr	a2, icountlevel\n\t"
-			     "movi	a2, 0\n\t"
-			     "wsr	a2, icount\n\t"
-#if XCHAL_NUM_IBREAK > 0
-			     "wsr	a2, ibreakenable\n\t"
-#endif
-#if XCHAL_HAVE_LOOPS
-			     "wsr	a2, lcount\n\t"
-#endif
-			     "movi	a2, 0x1f\n\t"
-			     "wsr	a2, ps\n\t"
-			     "isync\n\t"
-			     "jx	%0\n\t"
-			     :
-			     : "a" (XCHAL_RESET_VECTOR_VADDR)
-			     : "a2");
-
+	cpu_reset();
 	/* control never gets here */
 }