am3505/3517: Skip TWL

In cpu.h, OMAP35XX_CLASS is currently defined as 0x35000034. the cpu_is_omap34xx() return 1 even on am3505 and am3517.

I'm not sure if the CPU class bits should be changed to 0x35 (redefining OMAP35XX_CLASS to 0x35000035). So instead, I'm adding code to explicitely ignore am3505 and am3517.

index 07d6140..13b9fbd 100644
@@ -266,7 +266,7 @@ int __init omap3_twl_init(void)
 {
 	struct voltagedomain *voltdm;
 
-	if (!cpu_is_omap34xx())
+	if (!cpu_is_omap34xx() || cpu_is_omap3505() || cpu_is_omap3517() )
 		return -ENODEV;
 
 	if (cpu_is_omap3630()) {