media: venus: hfi_plat: Add platform ops for getting number of VPP pipes

Starting from v6 we have one more hfi property which will be needed
to calculate buffer sizes/count for particular codec and session type.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>