nss-dp: switchdev: apply flag dependency directives

nss-dp: switchdev: apply flag dependency directives

The FDB roaming issues were observed on ipq807x and ipq60xx boards.
The fix depends on API exposed only when NSS_DP_PPE_SUPPORT is enabled.
However, this flag applies to above mentioned platforms only and is
causing the logs to be flooded on other QCA platforms, including ipq50xx,
with:

[   34.893418] nss-dp 39c00000.dp1 lan: cannot get VSI ID for port 1
[   34.898370] nss-dp 39c00000.dp1 lan: cannot get VSI ID for port 1
[   34.904598] nss-dp 39c00000.dp1 lan: cannot get VSI ID for port 1
[   34.910661] nss-dp 39c00000.dp1 lan: cannot get VSI ID for port 1

So let's apply a dependency on the NSS_DP_PPE_SUPPORT flag and contain
the patch code for ipq807x and ipq60xx within conditional directives.

Tested on: Linksys SPNMX56

Signed-off-by: George Moussalem <george.moussalem@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/17966
Signed-off-by: Robert Marko <robimarko@gmail.com>