octeontx2-af: Check whether ipolicers exists

While displaying ingress policers information in
debugfs check whether ingress policers exist in
the hardware or not because some platforms(CN9XXX)
do not have this feature.

Fixes: e7d89717

 ("octeontx2-af: cn10k: Debugfs support for bandwidth")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Rakesh Babu <rsaladi2@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>