Sums the contents of source registers Rs1 and Rs2,
then loads the result into AGU accumulator register.
The registers Rs1 and Rs2 are accessed via Port 5,
their banks are selected by the bank selectors BS5.
Takes 4 cycles to execute.
Example: AGU_RR ZERO 0x50 0x51
AGU P5
------
- 50
- 51
- 00
RR 00
NOT YET
AGU_RR ZERO 0x20 0x21
!! Sums the contents of registers 0x20
!! and 0x21 and loads the result to AGU
!! accumulator register.