ARM: mach-imx: tzic: Staticize *tzic_base

Fix the following sparse warning:

arch/arm/mach-imx/tzic.c:52:14: warning: symbol 'tzic_base' was not declared. Should it be static?

Also, remove the comment, as it does not apply for kernels newer than 3.2.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>