Rename RAM modules

mor1kx_spram is actually a dual port ram, as it has seperate read and
write ports.
A common notion for such a dual port RAM is "simple dual port ram",
in contrast to the type of dual port ram that has two seperate read
and write ports that's commonly referred to as a "true dual port ram".
This updates the RAM modules to follow this notion.
execute_alu: move decoding of adder control signals to decode
execute_alu: move decoding of multiply ops to decode
execute_alu: move decoding of div ops to mor1kx_decode
execute_alu: move decoding of shift ops to mor1kx_decode
execute_alu: move decoding of ffl1 ops to mor1kx_decode
espresso/ctrl: simplify execute_valid generation
prontoespresso/ctrl: simplify execute_valid generation