ArmPkg & ArmVirtPkg: Make PcdMonitorConduitHvc a dynamic PCD

The monitor call conduit is fixed for a platform firmware in
most scenarios. For a normal virtual machine guest firmware,
the default conduit is HVC. However, for Arm CCA the Realm
code must use SMC as the conduit.

To have a common code base for Guest/Virtual firmware to be used
by both normal VMs and Realm VMs, make PcdMonitorConduitHvc as a
dynamic PCD. This allows the firmware to detect if it is running
in a Realm and it can configure the PcdMonitorConduitHvc as FALSE
(i.e. to use SMC as the conduit when running in a Realm).

Also update the ArmVirtPkg/ArmVirtKvmTool.dsc workspace to move
the PcdMonitorConduitHvc in the PcdsDynamic section to prevent
the build from breaking.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>