soc: ti: add initial PRM driver with reset control support

Add initial PRM (Power and Reset Management) driver for TI OMAP class
SoCs. Initially this driver only supports reset control, but can be
extended to support rest of the functionality, like powerdomain
control, PRCM irq support etc.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>