* gencode.c (expand_opcode): Simplify and reorganize.
Eliminate "shift" parameter. Eliminate "4 bits at a time"
assumption. Flatten switch statement to a single level.
Add "eeee" token for even-numbered registers.
(bton): Delete.
(fsca): Use "eeee" token.
(ppi_moves): Rename to "expand_ppi_movxy". Do the ddt
[movx/movy] expansion here, as well as the ppi expansion.
(gensim_caselist): Accept 'eeee' along with 'nnnn'.