[RISCV] Use binary search to look up supported profiles. (#90767)

As the list of profiles grow, this will be a more efficient lookup.

Because the profile name is a prefix of the Arch string, we use
upper_bound to find the first profile that definitely comes after the
Arch string. If that isn't the first supported profile, we move back 1
profile and see if that profile is a prefix of our Arch string.