sms: Refactor sms_memory_read to prepare for additional mapper types
sms: Refactor sms_memory_read to prepare for additional mapper types

This also allows us to restrict the 1K protected-area to the Sega mapper.

JoppyFurr/Snepulator,JoppyFurr/Snepulator,JoppyFurr/Snepulator,JoppyFurr/Snepulator,JoppyFurr/Snepulator,JoppyFurr/Snepulator