[build] Make sbitmap code available to the driver

The ARM option parsing code uses sbitmap data structures to manage
features and upcoming patches will shortly need to use these bitmaps
within the driver.  This patch moves sbitmap.o from OBJS to
OBJS-libcommon to facilitate this.

The patch has no impact on targets that don't need this functionality,
since the object is part of an archive and will only be extracted if
needed.

	* Makefile.in (OBJS): Move sbitmap.o from here ...
	(OBJS-libcommon): ... to here.

From-SVN: r249285