RISC-V: Treat R_RISCV_CALL and R_RISCV_CALL_PLT as the same in check_relocs.

RISC-V: Treat R_RISCV_CALL and R_RISCV_CALL_PLT as the same in check_relocs.

In fact, we can treate these two relocation as the same one in the
riscv_elf_check_relocs.  I have heard that RISC-V lld had made this
improvement, and so had GNU AARCH64, they only need R_AARCH64_CALL26
for calls rather than two seperate relocations.

Beside, the following PLT issue for RISC-V 32-bit glibc seems to be
fixed by applying at least this patch.

<https://sourceware.org/pipermail/libc-alpha/2020-August/117214.html>

I have ran the toolchain regression, and everything seems fine for now.

	bfd/
	* elfnn-riscv.c (riscv_elf_check_relocs): Treat R_RISCV_CALL
	and R_RISCV_CALL_PLT as the same in the riscv_elf_check_relocs.
	(riscv_elf_relocate_section): Remove the R_RISCV_CALL for the
	unresolved reloc checks.

	ld/
	testsuite/ld-riscv-elf/lib-nopic-01a.s: Use R_RISCV_JAL rather
	than R_RISCV_CALL.
	testsuite/ld-riscv-elf/lib-nopic-01b.d: Likewise.
	testsuite/ld-riscv-elf/lib-nopic-01b.s: Likewise.