ArmPkg/BdsLib: Removed PSCI discoverability from the Linux loader

ArmPkg/BdsLib: Removed PSCI discoverability from the Linux loader

Some platforms might decide to not support PSCI in their FDT-aware Linux
system even if their firmware supports it.
It is the responsibility of the platform engineer to provide the appropriate FDT.

The PCD gArmTokenSpaceGuid.PcdArmPsciSupport is not required anymore.

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@15658 6f19259b-4bc3-4df7-8a09-765794883524