CORE-V: Remove versioning support for XCV Extensions
Created by: NandniJamnadas
* `bfd/elfxx-riscv.c`: Implement default versioning for `XCV` as `1.0`.
* `gas/testsuite/gas/riscv`: Updated all `XCV` tests to remove explicit
call of versioning in march string.
* `ld/testsuite/gas/riscv`: Updated all `XCV` tests to remove explicit
call of versioning in march string.