division/remainder can be replaced with bitshifts in `fatdrvce`

I noticed that division is used instead of bit shifts for getting the quotient/remainder by a power of 2.
`util_cluster_entry_to_block` does 32bit unsigned division by 128
`util_ceil_byte_size_to_block_size` does 32bit unsigned division and remainder by 512

I think it would be beneficial to rewrite these functions to use bit shifts as division is a very slow operation to perform.
