ARM: OMAP2+: Prevent potential crash if GPMC probe fails

If the GPMC probe fails, devices that use the GPMC (such as ethernet
chips, flash memories, etc) can still allocate a GPMC chip-select and
register the device. On the OMAP2420 H4 board, this was causing the
kernel to crash after the gpmc probe failed and the board attempted
to start networking. Prevent this by marking all the chip-selects as
reserved by default and only make them available for devices to request
if the GPMC probe succeeds.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>