ARM: OMAP: gpmc: don't create devices from initcall on DT

On DT driven boards, the gpmc node will match the driver. Hence, there's
no need to do that unconditionally from the initcall.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Tony Lindgren <tony@atomide.com>