ArmPlatformPkg: Fix and Implement ArmPlatformGetPrimaryCoreMpId

- Used correct PCD
- Implement the function for AArch64, BeagleBoard, CTA15A7

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14937 6f19259b-4bc3-4df7-8a09-765794883524
ArmPlatformPkg/ArmPlatformStackLib: Do not directly use PcdArmPrimaryCore

To make the code platform independent we should not use PcdArmPrimaryCore
in libraries other than the platform specific libraries.
Some platforms allow to change the primary core with external registers.
These platforms do not use PcdArmPrimaryCore to identify the primary CPU.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14938 6f19259b-4bc3-4df7-8a09-765794883524
ArmPlatformPkg/ArmVExpress-RTSM-AEMv8Ax4-foundation.dsc: Remove the Monitor stacks PCDs

We do not have (Secure) Monitor mode on AArch64.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14939 6f19259b-4bc3-4df7-8a09-765794883524