Consolidate strmhz() implementation

ARM, i386, m68k and ppc all have identical implementations of strmhz().
Other architectures don't provide this function at all.

This patch moves strmhz() into lib_generic, reducing code duplication
and providing a more unified API across architectures.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

include/common.h

diff --git a/include/common.h b/include/common.h
index 06ed278..de3d595 100644
--- a/include/common.h
+++ b/include/common.h
@@ -224,7 +224,6 @@
 int	checkboard    (void);
 int	checkflash    (void);
 int	checkdram     (void);
-char *	strmhz(char *buf, long hz);
 int	last_stage_init(void);
 extern ulong monitor_flash_len;
 int mac_read_from_eeprom(void);
@@ -615,6 +614,9 @@
 		__attribute__ ((format (__printf__, 2, 3)));
 int	vsprintf(char *buf, const char *fmt, va_list args);
 
+/* lib_generic/strmhz.c */
+char *	strmhz(char *buf, long hz);
+
 /* lib_generic/crc32.c */
 uint32_t crc32 (uint32_t, const unsigned char *, uint);
 uint32_t crc32_wd (uint32_t, const unsigned char *, uint, uint);