ARC: [plat-eznps] use schd.wft instruction instead of sleep at idle task

When HW threads are active we want CPU to enter idle state only
for the calling HW thread and not to put on sleep all HW threads
sharing this core. For this need the NPS400 got dedicated instruction
so only calling thread is entring sleep and all other are still awake
and can execute instructions.

Signed-off-by: Noam Camus <noamca@mellanox.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: reworked patch to not use inline ifdef but a new function itself]

arch/arc/kernel/process.c

@@ -92,7 +92,18 @@ void arch_cpu_idle(void)
 		:"I"(arg)); /* can't be "r" has to be embedded const */
 }
 
-#else
+#elif defined(CONFIG_EZNPS_MTM_EXT)	/* ARC700 variant in NPS */
+
+void arch_cpu_idle(void)
+{
+	/* only the calling HW thread needs to sleep */
+	__asm__ __volatile__(
+		".word %0	\n"
+		:
+		:"i"(CTOP_INST_HWSCHD_WFT_IE12));
+}
+
+#else	/* ARC700 */
 
 void arch_cpu_idle(void)
 {