Currently, if the GPMC driver fails to reserve memory when probed we will
call BUG() and the kernel will not boot. Instead of calling BUG(), return
an error from probe and allow kernel to boot.

Boot tested on AM335x beagle bone board and OMAP4430 Panda board.

V2 changes:
- Ensure that clock and memory resources are released on error.
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>