Arm backend: Add is_node_supported checks for 4 ops (#8209)

Remove unnecessary asserts from op_sigmoid and op_log
Add is_node_supported checks for 4 ops
For convolution, maxpool2d, avgpool2d, and sum.
The checks mostly target hardware constraints on
Ethos-U55, though convolution also checks for some
unsupported behavior.

Signed-off-by: Erik Lundell <erik.lundell@arm.com>