Make opcode cycles into a proper initialised array.

Shrinks gameyob.nds by 2 KiB.
mmu.cpp: readMemory, writeMemory: Constrain the range of the Game Boy memory address so that 'gcc' issues a jump table for the switch instead of a binary search. Adds 1 left shift, but removes 3 comparisons and 3 conditional jumps.
Move various hotspots that are too large for the ARM9 cache into the ARM9 ITCM (opcodes, memory accessors) and DTCM (opcode cycle count arrays).
Merge pull request #1 from Nebuleon/optimisations

Optimisations