RISC-V: display fcsr in debugger

What

Depends on !12693 (merged)

Display information of the fcsr in the debugger.

Why

Was very useful in trying to debug !12693 (merged) & !12694 (merged)

How

Fetch info about fcsr, frm, fflags. We display the mnemonic for the rounding mode, and highlight any active floating-point exception flags.

Manually testing the MR

Step through the code from running:

make -C src/risc_v risc-v-sandbox && ./src/risc_v/risc-v-sandbox debug --input tezt/tests/riscv-tests/generated/rv64ud-p-fcmp