[libre-riscv-dev] fault-only-first mode

[Luke Kenneth Casson Leighton]

https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#unit-stride-fault-only-first-loads

i'm recommending we add this mode to the (last remaining) predication
table as it is extremely useful, usually used on LD/ST, for
data-dependent processing.

i *think* we can also use this not just for data-dependent load/store
traps, it would be really useful on compares as well: