RISC-V: Clarify link behaviors of R_RISCV_32/64 relocations with ABS symbol.

RISC-V: Clarify link behaviors of R_RISCV_32/64 relocations with ABS symbol.

There are two improvements, which are all referenced to aarch64,

* R_RISCV_32 with non ABS symbol cannot be used under RV64 when making
  shard objects.

* Don't need dynamic relocation for R_RISCV_32/64 under RV32/RV64 when
  making shared objects, if the referenced symbol is local ABS symbol.

However, considering this link,
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/341

Seems like we should makes all R_RISCV_32/64 relocs with ABS symbol
that don't need any dynamic relocations when making the shared objects.
But anyway, I just sync the current behavior as aarch64 ld, in case
there are any unexpected behaviors happen.

Passed the gcc/binutils regressions in riscv-gnu-toolchain.

bfd/
    * elfnn-riscv.c (riscv_elf_check_relocs): Only allow R_RISCV_32 with ABS
    symbol under RV64.
    (riscv_elf_relocate_section): R_RISCV_32/64 with local ABS symbol under
    RV32/RV64 doesn't need any dynamic relocation when making shared objects.
    I just make the implementations similar to other targets, so that will be
    more easy to mainatain.
ld/
    * testsuite/ld-riscv-elf/data-reloc*: New testcases.
    * testsuite/ld-riscv-elf/ld-riscv-elf.exp: Added new data-reloc* testcases,
    and need to make ifunc-seperate* testcases work for rv32.
    * testsuite/ld-riscv-elf/ifunc-seperate-caller-nonplt.s: Likewise.
    * testsuite/ld-riscv-elf/ifunc-seperate-caller-plt.s: Likewise.