accounts/abi: support custom int slice types

On solidity contract I have "uint32 []" type, when abigen creates Go
bindings - they are also "[]uint32" type on Go side. Even though it
looks like it should work - the actual type of the data coming from
the chain is of type " []*big.Int".

When executing contract function from Go side - getting unmarshal error:
abi: cannot unmarshal []*big.Int in to []uint32

The fix is to create array with the correct type

This fixed the issue reported in: https://github.com/ethereum/go-ethereum/issues/2802