ARM: OMAP2+: make omap_dma_dev_info __initdata

Make this __initdata as it is only modified only during the initialisation
phase in the function omap2_system_dma_init_dev and after this it is not
referenced anywhere in the kernel.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>