staging/rdma/hfi1: Fix for generic I2C interface

The original I2C interface was geared for QSFP accesses. Modify
the interface to behave more like a generic I2C controller such
that reads and writes can accept multi-byte offsets. Removed
reads following writes and moved reset to top level.

Reviewed-by: Easwar Hariharan <easwar.hariharan@intel.com>
Reviewed-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Pablo Cacho <pablo.cacho@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>