ARM: OMAP2+: Drop legacy code for gpmc-smc91x.c

This code was only used by 2430sdp, 3430sdp, and n900 development
boards.

The 2430sdp is already device tree only, and all the users of the
3430sdp and n900 development boards are already booting in device
tree mode, so we can drop the legacy smc91x support.

Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>