PE/x86-64: Display PE relocation names

For PE/x86-64, display PE relocation names:

R_X86_64_64   -> IMAGE_REL_AMD64_ADDR64
R_X86_64_32   -> IMAGE_REL_AMD64_ADDR32.
rva32         -> IMAGE_REL_AMD64_ADDR32NB
R_X86_64_PC32 -> IMAGE_REL_AMD64_REL32
DISP32+1      -> IMAGE_REL_AMD64_REL32_1
DISP32+2      -> IMAGE_REL_AMD64_REL32_2
DISP32+3      -> IMAGE_REL_AMD64_REL32_3
DISP32+4      -> IMAGE_REL_AMD64_REL32_4
DISP32+5      -> IMAGE_REL_AMD64_REL32_5
secrel32      -> IMAGE_REL_AMD64_SECREL

bfd/

	* coff-x86_64.c (howto_table): Display PE relocation names.

gas/

	* testsuite/gas/cfi/reloc-pe-i386.d: Updated.
	* testsuite/gas/i386/x86-64-w64-pcrel.d: Likewise.