platform: Drop timer warm init and exit hooks

Now that driver lifecycle is managed from within the SBI timer core,
platforms need only to initialize the driver once during cold init.
Remove the remaining platform hooks that are no longer used.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

platform/template/platform.c

@@ -116,20 +116,12 @@ static int platform_ipi_init(bool cold_boot)
 }
 
 /*
- * Initialize platform timer for current HART.
+ * Initialize platform timer during cold boot.
  */
-static int platform_timer_init(bool cold_boot)
+static int platform_timer_init(void)
 {
-	int ret;
-
 	/* Example if the generic ACLINT driver is used */
-	if (cold_boot) {
-		ret = aclint_mtimer_cold_init(&mtimer, NULL);
-		if (ret)
-			return ret;
-	}
-
-	return 0;
+	return aclint_mtimer_cold_init(&mtimer, NULL);
 }
 
 /*