test/crypto: update PDCP HFN scenarios

test/crypto: update PDCP HFN scenarios

As per current framework of PDCP testing, app can only support
either HFN override or fixed session HFN values but not both.
Now to enable both, either we duplicate all PDCP cases(>100)
for both override and fixed HFN. It will look clumsy as the
number of cases will be very high without much value addition.

Now to overcome this, we can do HFN override for Downlink cases
and fixed HFN for uplink cases. This way we will not loose the
test coverage and there will not be duplicacy in the test cases.

Signed-off-by: Akhil Goyal <akhil.goyal@nxp.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>