ARM: keystone2: psc: introduce function to hold and release module in reset.

These are useful for modules that need to be held in reset and are
enabled for data to be loaded on to them. Typically these are
microcontrollers or other processing entities in the system.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>