tc-xgate.c: Replace R_XGATE_PCREL_X with BFD_RELOC_XGATE_PCREL_X

tc-xgate.c: Replace R_XGATE_PCREL_X with BFD_RELOC_XGATE_PCREL_X

Replace R_XGATE_PCREL_X with BFD_RELOC_XGATE_PCREL_X to silence GCC 10
warning:

gas/config/tc-xgate.c:1339:5: error: implicit conversion from ‘enum elf_xgate_reloc_type’ to ‘bfd_reloc_code_real_type’ {aka ‘enum bfd_reloc_code_real’} [-Werror=enum-conversion]
 1339 |     R_XGATE_PCREL_9);
      |     ^~~~~~~~~~~~~~~

	PR gas/26044
	* config/tc-xgate.c (md_apply_fix): Check BFD_RELOC_XGATE_PCREL_X
	instead of R_XGATE_PCREL_X.
	(xgate_parse_operand): Replace R_XGATE_PCREL_X with
	BFD_RELOC_XGATE_PCREL_X.