RISC-V: Imply 'Zicntr' and 'Zihpm' implicitly depended on 'Zicsr'

This commit adds support for ratified extensions:
'Zicntr' and 'Zihpm', Which are all implicitly depend on 'Zicsr'.

This is based on:
<https://github.com/riscv/riscv-isa-manual/releases/download/riscv-isa-release-056b6ff-2023-10-02/unpriv-isa-asciidoc.pdf>

bfd/ChangeLog:

	* elfxx-riscv.c:  Add 'Zicntr' and 'Zihpm' -> 'Zicsr'.
        (riscv_supported_std_z_ext) Add 'Zicntr' and 'Zihpm' to the list.