[MIPS] Allow 48Hz to be selected if CONFIG_SYS_SUPPORTS_ARBIT_HZ is set.

This allows a 48Hz clock to be selected on Malta and other systems.  Note
this not normally a sensible option as it results in rather high latencies
for some kernel stuff.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -1824,7 +1824,7 @@ choice
 	 Allows the configuration of the timer frequency.
 
 	config HZ_48
-		bool "48 HZ" if SYS_SUPPORTS_48HZ
+		bool "48 HZ" if SYS_SUPPORTS_48HZ || SYS_SUPPORTS_ARBIT_HZ
 
 	config HZ_100
 		bool "100 HZ" if SYS_SUPPORTS_100HZ || SYS_SUPPORTS_ARBIT_HZ