Remove some custom sections from RISC-V's default linker scripts

Remove some custom sections from RISC-V's default linker scripts

This was added so compressed loads could have smaller offsets for
accessing the data section, but the result was that writable sections
ended up in INITIAL_READONLY_SECTIONS.  This is a bad idea.  The fix is
to just remove this micro-optimization.

Thanks to Alan Morda for finding the problem!

ld/ChangeLog

2017-01-09  Palmer Dabbelt <palmer@dabbelt.com>
            Kito Cheng <kito.cheng@gmail.com>

        * emulparams/elf32lriscv-defs.sh (INITIAL_READONLY_SECTIONS):
        Removed.
        (SDATA_START_SYMBOLS): Likewise.