ARM: omap5: add ft_board_setup for dra7xx/am57xx

Adds the board specific ft_board_setup() functions that
are called when CONFIG_OF_BOARD_SETUP is defined. These functions
will currently just call the ft_cpu_setup() function.

Adds CONFIG_OF_BOARD_SETUP to the defconfig files
for dra72_evm, dra74_evm, and am57xx_evm.

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

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