board_f: powerpc: Use timer_init() instead of init_timebase()

There is no good reason to use a different name on PowerPC. Change it to
timer_init() like the others.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: York Sun <york.sun@nxp.com>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/powerpc/lib/time.c

@@ -60,7 +60,7 @@ unsigned long ticks2usec(unsigned long ticks)
 #endif
 /* ------------------------------------------------------------------------- */
 
-int init_timebase (void)
+int timer_init(void)
 {
 	unsigned long temp;