OvmfPkg/IoMmuDxe: generalize IoMmuUnmap() to IoMmuUnmapWorker()

OvmfPkg/IoMmuDxe: generalize IoMmuUnmap() to IoMmuUnmapWorker()

IoMmuUnmapWorker() is identical to IoMmuUnmap(), it just takes an
additional BOOLEAN parameter called "MemoryMapLocked".  If the memory map
is locked, IoMmuUnmapWorker() does its usual job, but it purposely leaks
memory rather than freeing it. This makes it callable from
ExitBootServices() context.

Turn IoMmuUnmap() into a thin wrapper around IoMmuUnmapWorker() that
passes constant FALSE for "MemoryMapLocked".

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Tested-by: Brijesh Singh <brijesh.singh@amd.com>