(MESS) c64: some optimizations [Alex Jackson]
 * read_pla() leaves the PLA outputs packed, instead of using eight output parameters to return them
 * flatten nested switch statements in read_memory() and write_memory()
 * mos6566: inline bus_r() and various READ_LINE_MEMBERs

(nw)
from 285% to 300% idling at basic prompt with default slot devices (c1541, no cartridge)
About half the speedup comes from read_pla() refactoring, the other half comes from flattening the switch()es.