CSKY: Add ck803r2 series cpu.

gas/
        * config/tc-csky.c (CSKY_ISA_803R2): New.
        (csky_archs): Add ck803r2 series.
        (md_begin): Fix warning about -medsp.
        (csky_get_freg_val): Support lowercase of fpu register name.
        * testsuite/gas/csky/cskyv2_ck803r2.s: New file.
        * testsuite/gas/csky/cskyv2_ck803r2.d: New file.

include/
        * csky.h (CSKYV2_ISA_3E3R2): New.

opcodes/
        * csky-opc.h (csky_v2_opcodes): Add instruction bnezad.