OMAP: CM: Move MAX_MODULE_READY_TIME to cm.h

The maximum timeout to wait for the PRCM to request that a module
exit idle or reach functionnal state is common to OMAP2/3/4 SoCs,
so, move it to the chip family-common cm.h include file.

Reduce the timeout from 20 ms to 2 ms.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>