65816 FPI memory access should be fast

[samkusin]

Certain I/O registers are read from FPI vs MEGA2 regions and should FPI time vs MEGA2 time taken per access.
Currently all Cx00 I/O space accesses memory "slowly". Differentiate between certain accesses and apply fast timing to those accesses.
ROM is accessed fast currently - this just applies to Cx00.
These registers are documented in the HW reference.