OMAP1: SRAM: fix size for OMAP1611 SoCs

Kernel was failing to boot on omap1611 based OSK boards due to
mis-configured SRAM size.  Existing code was using a hard-coded value
for 250k, which was then rounded down by PAGE_SIZE.  Increasing this to
256k allows kernel to boot on omap1611 SoCs.

Problem reported by and initial fix suggested by Tim Bird.

Thanks to Tony Lindgren for helping diagnose the problem to being
specific to OMAP1611 and not affecting OMAP1610/OMAP1623.

Reported-by: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>