scp: Introduce css_scp_system_off() function

The common implementation of css_scp_sys_shutdown and
css_scp_warm_reset is refactored into a new function,
css_scp_system_off() that allows the desired power state to be
specified.

The css_scp_system_off can be used in the implementation of
SYSTEM_RESET2 for PSCI v1.1.

Change-Id: I161e62354d3d75f969b8436d794335237520a9a4
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/plat/arm/css/drivers/scp/css_scp.h b/plat/arm/css/drivers/scp/css_scp.h
index 223e372..4a6d473 100644
--- a/plat/arm/css/drivers/scp/css_scp.h
+++ b/plat/arm/css/drivers/scp/css_scp.h
@@ -21,6 +21,7 @@
 int css_scp_get_power_state(u_register_t mpidr, unsigned int power_level);
 void __dead2 css_scp_sys_shutdown(void);
 void __dead2 css_scp_sys_reboot(void);
+void __dead2 css_scp_system_off(int state);
 
 /* API for SCP Boot Image transfer. Return 0 on success, -1 on error */
 int css_scp_boot_image_xfer(void *image, unsigned int image_size);