riscv: Make contribs build again.

riscv: Make contribs build again.

The issue was that the LINKAGE_TEMP_REG being NL3 was a C argument
register, so of course that caused clashing on C call-out, causing
problems with run-program. Going back to NL7 didn't work either
because it wasn't getting saved before entry into the trampoline. The
code here used to have NL7 before the trampoline code was gutted and
then restored, so I'm wondering how this ever worked before, because
it definitely did. Pick LIP as the TEMP_REG now because not only does
it get saved, it's also the least likely thing to get disturbed by
clobbering.

Fixes #lp2002930.

Also remove assembly routine printing because it doesn't need to be
part of the build script (unlike the other files in output/ which
can't trivially be recovered from a built image), and because not all
disassembler printers have been written on riscv yet.