Removing dead MACH_U300_BS26

MACH_U300_BS26 doesn't exist in Kconfig, therefore removing all
references for it from the source code.

Signed-off-by: Christoph Egger <siccegge@cs.fau.de>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>