powerpc/SECURE_BOOT: Add PAMU driver

PAMU driver basic support for usage in Secure Boot.
In secure boot PAMU is not in bypass mode. Hence to use
any peripheral (SEC Job ring in our case), PAMU has to be
configured.

The patch reverts commit 7cad2e38.

The Header file pamu.h and few functions in driver have been derived
from Freescale Libos.

Signed-off-by: Ruchika Gupta <ruchika.gupta@nxp.com>
Signed-off-by: Aneesh Bansal <aneesh.bansal@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>