target/alpha: Clean up alpha_cpu_dump_state

Drop the "RI" and "FIR" prefixes; use only the normal linux names.
Add the FPCR to the dump.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>