OvmfPkg: CsmSupportLib: Set/use platform specific legacy interrupt device

OvmfPkg: CsmSupportLib: Set/use platform specific legacy interrupt device

Use a PCD set from PEI to determine the legacy interrupt device
number appropriate for the underlying platform type during protocol
initialization.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16375 6f19259b-4bc3-4df7-8a09-765794883524