[PATCH] arm26: select system type via "choice"

Choosing ARCH_ARC and ARCH_A5K together causes redefining and errors
here and there.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Ian Molton <spyro@f2s.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>