This patch updates existing macros, functions used for TI816X, to enable
addition of other SoCs belonging to TI81XX family (e.g., TI814X).

The approach taken is to use TI81XX/ti81xx for code/data going to be common
across all TI81XX devices.

cpu_is_ti81xx() is introduced to handle code common across TI81XX devices.

In addition, ti8168_evm_map_io() is now replaced with ti81xx_map_io() and moved
in mach-omap2/common.c as same will be used for TI814X and is not board
specific.

Signed-off-by: Hemant Pedanekar <hemantp@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>