arm: socfpga: agilex5: Add new driver model for system manager in Agilex5

arm: socfpga: agilex5: Add new driver model for system manager in Agilex5

Initial creation of new system manager driver.

Add supports for the SOCFPGA System Manager Register block which
aggregates different peripheral function into one area.
On 64 bit ARM parts, the system manager only can be accessed during
EL3 mode, this driver model provide user the high level access
to system register and abstract user from low level access.

The base address of system manager can be retrieved
using DT framework through the System Manager driver.

Signed-off-by: Tien Fong Chee <tien.fong.chee@altera.com>
Signed-off-by: Boon Khai Ng <boon.khai.ng@altera.com>