ARM: imx27: Remove imx27_soc_init()

imx27_soc_init() was only used by i.MX27 board files. Since the
board files users are gone, it is safe to remove imx27_soc_init() too.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>