ARMv8: Add support for poweroff via PSCI

Add support for calling poweroff in case of psci is wired.
Based on the same solution as is used for reset.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[trini: Move all logic in to fwcall.c as other ARMs implement poweroff
via PMIC]
Signed-off-by: Tom Rini <trini@konsulko.com>

arch/arm/cpu/armv8/fwcall.c

@@ -1,5 +1,6 @@
 /**
  * (C) Copyright 2014, Cavium Inc.
+ * (C) Copyright 2017, Xilinx Inc.
  *
  * SPDX-License-Identifier:	GPL-2.0+
 **/
@@ -114,6 +115,22 @@ void __noreturn __efi_runtime psci_system_off(void)
 		;
 }
 
+#ifdef CONFIG_CMD_POWEROFF
+int do_poweroff(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	puts("poweroff ...\n");
+
+	udelay(50000); /* wait 50 ms */
+
+	disable_interrupts();
+
+	psci_system_off();
+
+	/*NOTREACHED*/
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_PSCI_RESET
 void reset_misc(void)
 {