net: ipa: FLAVOR_0 register doesn't exist until IPA v3.5

The FLAVOR_0 version first appears in IPA v3.5, so avoid attempting
to read it for versions prior to that.

This register contains a concise definition of the number and
direction of endpoints supported by the hardware, and without it
we can't verify endpoint configuration in ipa_endpoint_config().
In this case, just indicate that any endpoint number is available
for use.

Originally proposed by AngeloGioacchino Del Regno.

Link: https://lore.kernel.org/netdev/20210211175015.200772-3-angelogioacchino.delregno@somainline.org


Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: AngeloGioacchino Del Regno
Signed-off-by: David S. Miller <davem@davemloft.net>