OMAP3: add comments for erratas i540 and i478 workarounds

Add comments and IDs for the following erratas:
- i540: MPU cannot exit from Standby,
- i478: Unexpected Cold-Reset is generated when device is coming
   back from OFF mode

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/irq.c

@@ -284,7 +284,10 @@ void omap3_intc_suspend(void)
 
 void omap3_intc_prepare_idle(void)
 {
-	/* Disable autoidle as it can stall interrupt controller */
+	/*
+	 * Disable autoidle as it can stall interrupt controller,
+	 * cf. errata ID i540 for 3430 (all revisions up to 3.1.x)
+	 */
 	intc_bank_write_reg(0, &irq_banks[0], INTC_SYSCONFIG);
 }