OvmfPkg PlatformBdsLib: Set SCI_EN bit of PMCNTRL

OvmfPkg PlatformBdsLib: Set SCI_EN bit of PMCNTRL

If the bit is not set, then the only method ACPI defines
for setting it is to use the SMI SCI enable code path.

Since OVMF does not support SMM, we must enable the
bit during boot.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Erik Bjorge <erik.c.bjorge@intel.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Bei Guan <gbtju85@gmail.com>
Reviewed-by: Bei Guan <gbtju85@gmail.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13278 6f19259b-4bc3-4df7-8a09-765794883524