uboot-imx

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>