OMAP3: PM: Wait for SDRC ready iso a blind delay

This patch improves the wakeup SRAM code polling the SDRC to become ready
instead of just waiting for a fixed amount of time.

Signed-off-by: Peter 'p2' De Schrijver <peter.de-schrijver@nokia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>