ARM: SMP: Refactor Kconfig to be more maintainable

Making SMP depend on (huge list of MACH_ and ARCH_ configs) is
bothersome to maintain and likely to lead to merge conflicts.

This patch moves the knowledge of which platforms are SMP-capable
to the individual machines.  To enable this, a new HAVE_SMP config
option is introduced to allow machines to indicate that they can
run in a SMP configuration.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
        (for nomadik, ux500)
Acked-by: Tony Lindgren <tony@atomide.com>
        (for omap)
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
        (for exynos)
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
        (for imx)
Acked-by: Olof Johansson <olof@lixom.net>
        (for tegra)