omap: Don't enable GPMC CS0 with nothing attached

omap: Don't enable GPMC CS0 with nothing attached

If CONFIG_(NAND|NOR|ONENAND) is not defined, no configuration is set
for GPMC on chip select #0---size is 0.  In this case, the GPMC
configuration should be reset but not enabled.  Enabling causes the
Gumstix DuoVero board to hang when entering Linux.

Signed-off-by: Ash Charles <ashcharles@gmail.com>
[trini: Switch to testing base as GPMC_SIZE_256M is 0x0]
Signed-off-by: Tom Rini <trini@ti.com>