stmmac: Make time functionality depend upon RTC_HCTOSYS_DEVICE

Based upon a report by Stephen Rothwell.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/stmmac/Kconfig

@@ -32,6 +32,7 @@ config STMMAC_DUAL_MAC
 config STMMAC_TIMER
 	bool "STMMAC Timer optimisation"
 	default n
+	depends on RTC_HCTOSYS_DEVICE
 	help
 	  Use an external timer for mitigating the number of network
 	  interrupts. Currently, for SH architectures, it is possible