arm: socfpga: mailbox: Notify SDM on HPS code execution stages

arm: socfpga: mailbox: Notify SDM on HPS code execution stages

Introducing a new mailbox command "HPS_STAGE_NOTIFY" to notify Secure
Device Manager (SDM) on the stage of HPS code execution.

Generally, there are three main code execution stages: First Stage Boot
Loader (FSBL) which is U-Boot SPL, Second Stage Boot Loader (SSBL) which
is U-Boot, and the Operating System (OS) which is Linux.

This enables the user to query the SDM for HPS error details.

Signed-off-by: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi@altera.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@altera.com>