[MIPS] Don't use genrtc.

The only pseudo-legitimate MIPS user of genrtc was a systems that doesn't
have an RTC in hardware at all.  At this point faking one is a little
pointless ...
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index ef683eb..a31c6d2 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -815,7 +815,7 @@
 
 config GEN_RTC
 	tristate "Generic /dev/rtc emulation"
-	depends on RTC!=y && !IA64 && !ARM && !M32R && !SPARC && !FRV && !S390 && !SUPERH
+	depends on RTC!=y && !IA64 && !ARM && !M32R && !MIPS && !SPARC && !FRV && !S390 && !SUPERH
 	---help---
 	  If you say Y here and create a character special file /dev/rtc with
 	  major number 10 and minor number 135 using mknod ("man mknod"), you