sim_core: fix rcall instruction cycles...

Based on the instrtiming.elf code and checking the Avr Instruction
 Manual, RCALL was found to be producing incorrect cycle counts.

Atmega; 3, 16-bit pc; 4, 22-bit pc.

Fixed accordingly.

	modified:   sim/sim_core.c
Merge pull request #68 from bsekisser/master-core-fix-rcall-cycles

sim_core: fix rcall instruction cycles...