ARM: omap5: add hooks for cpu/SoC fdt fixups

Adds an fdt.c file in that defines the ft_cpu_setup() function,
which should be called from a board-specific ft_board_setup()).
This ft_cpu_setup() will currently do nothing for non-secure (GP)
devices	but contains pertinent updates for booting on secure (HS)
devices.

Update the omap5 Makefile to include the fdt.c in the build.

Signed-off-by: Daniel Allred <d-allred@ti.com>
Signed-off-by: Madan Srinivas <madans@ti.com>

Reviewed-by: Tom Rini <trini@konsulko.com>