powerpc/5xxx: Add common mpc5xxx_get_bus_frequency() function

So far, MPC512x used mpc512x_find_ips_freq() to get the bus frequency,
while MPC52xx used mpc52xx_find_ipb_freq().  Despite the different
clock names (IPS vs. IPB) the code was identical.

Use common code for both processor families.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/sysdev/Makefile

@@ -50,6 +50,9 @@ obj-$(CONFIG_PPC_DCR)		+= dcr.o
 obj-$(CONFIG_8xx)		+= mpc8xx_pic.o cpm1.o
 obj-$(CONFIG_UCODE_PATCH)	+= micropatch.o
 
+obj-$(CONFIG_PPC_MPC512x)	+= mpc5xxx_clocks.o
+obj-$(CONFIG_PPC_MPC52xx)	+= mpc5xxx_clocks.o
+
 ifeq ($(CONFIG_SUSPEND),y)
 obj-$(CONFIG_6xx)		+= 6xx-suspend.o
 endif