Add context save and restore for PRCM module to support off-mode.
Additional registers (CM_CLKSEL4, CM_CLKEN, CM_CLKEN2) added by Tero
Kristo.

Missing CM_CLKEN_PLL_IVA2 register added by Kalle Jokiniemi.
Signed-off-by: NRajendra Nayak <rnayak@ti.com>
Signed-off-by: NTero Kristo <tero.kristo@nokia.com>
Signed-off-by: NKalle Jokiniemi <kalle.jokiniemi@digia.com>
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>